Signalling pathways regulating inducible nitric oxide synthase expression in human kidney epithelial cells

Evaluation of the protective effect of edaravone on doxorubicin nephrotoxicity by [99mTc]DMSA renal scintigraphy and biochemical methods

To evaluate the nephroprotective effect of edaravone on doxorubicin-induced nephrotoxicity. In this experimental study, twenty-eight Wistar male rats were used. The rats were separated into 4 groups (n = 7); group І (control), rats were treated with saline (4 ml/kg) and group ІІ (doxorubicin), nephrotoxicity was induced by three doses of 18 mg/kg/i.p. doxorubicin, at a 24-h interval on the 12th, 13th, and 14th days. Group ІІІ (edaravone), rats were treated with edaravone (30 mg/kg/for 14 days), and group ІV (edaravone + doxorubicin), rats were treated with edaravone (30 mg/kg/for 14 days) and doxorubicin were injected (18 mg/kg/for 3 days; at a 24-h interval on the 12th, 13th, and 14th days). On the 15th day of the experiment, technetium-99m-labeled dimercaptosuccinic acid ([^99mTc]DMSA) uptake was obtained in both kidneys and biochemical parameters from serum and kidney tissue were measured. Doxorubicin led to nephrotoxicity through elevation of serum blood urea nitrogen (BUN), creatinine and tumor necrosis factor-α (TNF-α), nitric oxide (NO), and interleukin-6 (IL-6) in kidney tissue and decreased [^99mTc]DMSA uptake level in the kidney when compared with control group (p < 0.01). Pretreatment edaravone significantly decreased BUN and creatinine, also kidney tissue TNF-α, IL-6, NO, and increased [^99mTc]DMSA uptake level compared with the doxorubicin. Edaravone has a significant nephroprotective effect through the attenuation of oxidative stress and inflammatory markers during doxorubicin-induced nephrotoxicity in rats.

Host-Derived Nitric Oxide and Its Antibacterial Effects in the Urinary Tract

Urinary tract infection (UTI) is one of the most common bacterial infections in humans, and the majority are caused by uropathogenic Escherichia coli (UPEC). The rising antibiotic resistance among UPEC and the frequent failure of antibiotics to effectively treat recurrent UTI and catheter-associated UTI motivate research on alternative ways of managing UTI. Abundant evidence indicates that the toxic radical nitric oxide (NO), formed by activation of the inducible nitric oxide synthase, plays an important role in host defence to bacterial infections, including UTI. The major source of NO production during UTI is from inflammatory cells, especially neutrophils, and from the uroepithelial cells that are known to orchestrate the innate immune response during UTI. NO and reactive nitrogen species have a wide range of antibacterial targets, including DNA, heme proteins, iron-sulfur clusters, and protein thiol groups. However, UPEC have acquired a variety of defence mechanisms for protection against NO, such as the NO-detoxifying enzyme flavohemoglobin and the NO-tolerant cytochrome bd-I respiratory oxidase. The cytotoxicity of NO-derived intermediates is nonspecific and may be detrimental to host cells, and a balanced NO production is crucial to maintain the tissue integrity of the urinary tract. In this review, we will give an overview of how NO production from host cells in the urinary tract is activated and regulated, the effect of NO on UPEC growth and colonization, and the ability of UPEC to protect themselves against NO. We also discuss the attempts that have been made to develop NO-based therapeutics for UTI treatment.

Samchuleum attenuates diabetic renal injury through the regulation of TGF‑β/Smad signaling in human renal mesangial cells

Renal mesangial cell proliferation is a major clinical feature of diabetic nephropathy (DN) and includes glomerulosclerosis and renal fibrosis. Samchuleum (SCE) is a traditional herbal mixture that is recorded in the ancient Korean medical book, Donguibogam. The present study attempted to determine whether SCE treatment was able to improve high glucose (HG)‑induced mesangial cell fibrosis and glomerulosclerosis in primary cultured human mesangial cells. Thymidine incorporation under HG induction was increased, but was decreased by SCE in a dose dependent manner. Pretreatment with SCE led to a downregulation in the expression of cyclins and cyclin‑dependent kinases (CDKs), and an upregulation of the CDK inhibitors, p21waf1/cip1 and p27kip1. In addition, SCE exposure markedly suppressed the reactive oxygen species signaling pathway under HG conditions. HG enhanced the expression levels of fibrosis‑promoting mediators, including collagen IV and connective tissue growth factor, which were markedly attenuated by SCE. SCE treatment inhibited HG‑induced fibronectin mRNA expression and decreased the expression of transforming growth factor (TGF)‑β1, Smad‑2 and Smad‑4, whereas Smad‑7 expression increased under HG. SCE treatment induced the degradation of the extracellular matrix by blocking TGF‑β1/Smad signaling. Therefore, the present study suggested that the inhibitory effect of SCE on mesangial proliferation and renal fibrosis may be an effective therapy in the treatment of renal dysfunction leading to DN.

Expression and Differential Responsiveness of Central Nervous System Glial Cell Populations to the Acute Phase Protein Serum Amyloid A

Acute-phase response is a systemic reaction to environmental/inflammatory insults and involves hepatic production of acute-phase proteins, including serum amyloid A (SAA). Extrahepatically, SAA immunoreactivity is found in axonal myelin sheaths of cortex in Alzheimer's disease and multiple sclerosis (MS), although its cellular origin is unclear. We examined the responses of cultured rat cortical astrocytes, microglia and oligodendrocyte precursor cells (OPCs) to master pro-inflammatory cytokine tumour necrosis factor (TNF)-α and lipopolysaccaride (LPS). TNF-α time-dependently increased Saa1 (but not Saa3) mRNA expression in purified microglia, enriched astrocytes, and OPCs (as did LPS for microglia and astrocytes). Astrocytes depleted of microglia were markedly less responsive to TNF-α and LPS, even after re-addition of microglia. Microglia and enriched astrocytes showed complementary Saa1 expression profiles following TNF-α or LPS challenge, being higher in microglia with TNF-α and higher in astrocytes with LPS. Recombinant human apo-SAA stimulated production of both inflammatory mediators and its own mRNA in microglia and enriched, but not microglia-depleted astrocytes. Co-ultramicronized palmitoylethanolamide/luteolin, an established anti-inflammatory/ neuroprotective agent, reduced Saa1 expression in OPCs subjected to TNF-α treatment. These last data, together with past findings suggest that co-ultramicronized palmitoylethanolamide/luteolin may be a novel approach in the treatment of inflammatory demyelinating disorders like MS.

Oryeongsan suppressed high glucose-induced mesangial fibrosis

Background

The pathological change of kidney in diabetic nephropathy is represented hypertrophy, inflammation, and renal fibrosis. Oryeongsan, traditional oriental herbal formula, is widely used for the treatment of nephrosis, dropsy, and uremia. This study was examined whether Oryeongsan attenuate high-glucose (HG)-promoted rat mesangial cell fibrosis and matrix accumulation, major features of diabetic glomerulosclerosis.

Methods

Oryeongsan was mixed traditional herbal medicine, Alisma orientale Juz, Polyporus umbellatus Fries, Atractylodes macrocephala Koidez, Poria cocos Wolf and Cinnamomum Cassia Presl (5:3:3:1). Renoprotective role in diabetic nephropathy of Oryeongsan was evaluated by [³H]-thymidine incorporation, Western blot, RT-qPCR and immunofluorescence microscopy assay.

Results

Rat mesangial cell proliferation induced by HG was significantly accelerated, which was inhibited by Oryeongsan in a dose dependent manner. HG enhanced expression of fibrosis biomarkers such as collagen IV and connective tissue growth factor (CTGF), which was markedly attenuated by Oryeongsan. Oryeongsan increased HG-inhibited membrane type-1 matrix metalloproteinase expression (MT1-MMP) and MMP-2 promotor activity, whereas suppressed HG-induced tissue inhibitor of matrix metalloproteinase-2 (TIMP-2) expression. Moreover, Oryeongsan promoted extracellular matrix degradation through disturbing transforming growth factor β (TGF-β)–Smad signaling. This study further revealed that Oryeongsan ameliorated HG-induced mesangial inflammation accompanying induction of intracellular cell adhesion molecule-1 (ICAM-1) and monocyte chemoattractant protein-1 (MCP-1). Moreover, pretreatment of Oryeongsan inhibited NF-κB translocation in HG-exposed mesangial cell.

Conclusion

These results demonstrate that Oryeongsan has protective effect against renal proliferation, fibrosis, and inflammation. Therefore Oryeongsan may be specific therapies targeting renal dysfunction leading to diabetic nephropathy.

Positive feedback regulation of human inducible nitric-oxide synthase expression by Ras protein S-nitrosylation

The production of nitric oxide (NO) by inducible NO synthase (iNOS) regulates many aspects of physiology and pathology. The expression of iNOS needs to be tightly regulated to balance the broad ranging properties of NO. We have investigated the feedback regulation of cytokine-induced iNOS expression by NO in human cells. The pharmacological inhibition of iNOS activity reduced iNOS protein levels in response to cytokine stimulation in a human epithelial cell line (A549 cells) as well as in primary human astrocytes and bronchial epithelial cells. The addition of exogenous NO using a NO donor prevented the reduction in iNOS levels caused by blockade of iNOS activity. Examination of signaling pathways affected by iNOS indicated that NO S-nitrosylated Ras. Transfection of cells with a S-nitrosylation-resistant Ras mutant reduced iNOS protein levels, indicating a role for this Ras modification in the amplification of iNOS levels. Further, the induction of iNOS protein levels correlated with the late activation of the phosphatidylinositol 3-kinase/Akt and mammalian target of rapamycin (mTOR) pathways, and inhibition of these signaling molecules reduced iNOS levels. Altogether, our findings reveal a previously unknown regulatory pathway that amplifies iNOS expression in human cells.

Polydatin ameliorates experimental diabetes-induced fibronectin through inhibiting the activation of NF-κB signaling pathway in rat glomerular mesangial cells

A number of studies have recently demonstrated the involvement of nuclear factor-kappa B (NF-κB) activation and the subsequent coordinated inflammatory responses in the pathogenesis of diabetic nephropathy (DN). Polydatin has been shown to have the ability of anti-adhesive inflammation. However, the possible protective and beneficial effects of polydatin on DN via suppressing inflammatory damage and extracellular matrix (ECM) accumulation are not fully elucidated. We found that the polydatin could inhibit the induction and activity of NF-κB, and meanwhile ameliorating ECM accumulation in streptozotocin-diabetic rats. We aimed to investigate the effect of polydatin on fibronectin (FN) protein expression, and to elucidate its potential mechanism involving the NF-κB inflammatory signaling pathway in rat glomerular mesangial cells (GMCs) cultured under high glucose. The results revealed that polydatin significantly suppressed high glucose-induced FN production, inhibited NF-κB nuclear translocation, reduced the DNA-binding activity of NF-κB, as well as decreased the protein expression of ICAM-1 and TGF-β in GMCs. These findings suggested that polydatin significantly represses high glucose-induced FN expression in rat GMCs, which may be closely related to its inhibition of the NF-κB signaling pathway. Hence, we elucidated the potential mechanisms of the anti-inflammatory effects and ECM accumulation alleviation of polydatin in GMCs of DN in vitro.

Pressure activates epidermal growth factor receptor leading to the induction of iNOS via NFkappaB and STAT3 in human proximal tubule cells

Ureteral obstruction leads to increased pressure and inducible nitric oxide synthase (iNOS) expression. This study examined the involvement of epidermal growth factor (EGF) receptor (EGFR), nuclear factor-kappaB (NFkappaB), and signal transducers and activators of transcription 3 (STAT3) in iNOS induction in human proximal tubule (HKC-8) cells in response to pressure or EGF. HKC-8 cells were subjected to 60 mmHg pressure or treated with EGF for 0-36 h. iNOS was more rapidly induced in response to EGF than pressure. The addition of EGFR, NFkappaB, and STAT3 inhibitors significantly suppressed pressure- or EGF-stimulated iNOS mRNA and protein expression. Analysis of the activated states of EGFR, NFkappaB p65, and STAT3 after exposure to both stimuli demonstrated phosphorylation within 2.5 min. Anti-EGF antibody inhibited iNOS induction in pressurized HKC-8 cells, providing evidence that endogenous EGF mediates the response to pressure. In ureteral obstruction, when pressure is elevated, phosphorylated EGFR was detected in the apical surface of the renal tubules, validating the in vitro findings. These data indicate that EGFR, NFkappaB, and STAT3 are required for human iNOS gene induction in response to pressure or EGF, indicating a similar mechanism of activation.

Cytokine-induced epithelial permeability changes are regulated by the activation of the p38 mitogen-activated protein kinase pathway in cultured Caco-2 cells

Increased intestinal/epithelial permeability in sepsis and endotoxemia has been noted to be induced by proinflammatory cytokines such as interferon-gamma, TNF-alpha, and IL-1beta. The p38 mitogen-activated protein kinase (MAPK) signaling pathway plays an important role in regulating the inflammatory response induced by these cytokines. We tested the hypothesis that epithelial permeability changes are regulated through the p38 MAPK signaling pathway. Caco-2 cells were cultured for 21 days and then stimulated with a cytokine mixture (CytoMix: TNF-alpha, interferon-gamma, and IL-1beta). Epithelial barrier function was evaluated by measuring permeability in an Ussing chamber. CytoMix-induced changes of MAPKs (p38, c-Jun amino-terminal kinase, and extracellular-regulated kinase), NO production, and inflammatory responses (IL-6 and IL-8 levels) were also assessed. The signaling pathways were further studied by pretreating cells with SB203580, a specific p38 MAPK inhibitor. CytoMix increased permeability at 24 and 48 h but not at 4 h. This was associated with increased IL-6 and IL-8 production, as well as increases in phosphorylation of all three MAPKs. Treatment with SB203580 completely blocked p38 activity with transient inhibition of p38 phosphorylation. SB203580 also prevented the CytoMix-induced permeability increase and reduced NO, IL-6, and IL-8 levels. The results suggest that p38 MAPK plays an important role in regulating epithelial barrier function during inflammation.

Involvement of iNOS and NO in TNF-alpha-downregulated resistin gene expression in 3T3-L1 adipocytes

OBJECTIVE

In order to characterize the regulation of resistin gene expression, we explore the effect of tumornecrosis factor-alpha (TNF-alpha) on resistin mRNA expression and its underlying mechanism in 3T3-L1 adipocytes.

METHODS AND PROCEDURES

Differentiated 3T3-L1 adipocytes were treated for 24 h with 0-10 ng/ml of TNF-alpha or with 2.5 ng/ml of TNF-alpha for 0-24 h, and then resistin mRNA levels were measured by northern blotting. To further explore the involvement of nitric oxide (NO) in TNF-alpha-regulated resistin expression, the effect of the NO donor, sodium nitroprusside (SNP), on resistin mRNA levels in adipocytes and the effect of the nitric oxide synthase (NOS) inhibitors, N(G)-nitro-L-arginine methyl ester (L-NAME), and S,S'-1,3-phenylene-bis(1,2-ethanediyl)-bis-isothiourea.2HBr (PBITU), on the TNF-alpha effect in adipocytes were examined. The effects of TNF-alpha on inducible NOS (iNOS) protein expression in adipocytes were also measured by western blotting.

RESULTS

Our results showed that TNF-alpha caused a dose-dependent reduction in resistin mRNA levels. This effect seemed to be associated with the TNF-alpha-induced expression of iNOS. The results showed that TNF-alpha induced iNOS expression and release of NO after 24-h treatment of differentiated 3T3-L1 adipocytes. Pretreatment with L-NAME and PBITU significantly reversed the TNF-alpha-induced downregulation of resistin expression, while treatment with SNP mimicked the inhibitory effect of TNF-alpha on resistin expression. In addition, pretreatment with protein tyrosine kinase (PTK) inhibitors, genistein and AG-1288, prevented TNF-alpha-induced iNOS expression and subsequent resistin downregulation.

DISCUSSION

Our data suggest that TNF-alpha suppresses resistin expression by inducing iNOS expression, thus causing overproduction of NO, which downregulates resistin gene expression.

Tumor necrosis factor alpha-mediated nitric oxide production enhances manganese superoxide dismutase nitration and mitochondrial dysfunction in primary neurons: an insight into the role of glial cells

Tumor necrosis factor-alpha (TNF-alpha), a ubiquitous pro-inflammatory cytokine, is an important mediator in the immune-neuroendocrine system that affects the CNS. The present study demonstrates that treatment with TNF-alpha activates microglia to increase TNF-alpha production in primary cultures of glial cells isolated from wild-type (WT) mice and mice deficient in the inducible form of nitric oxide synthase (iNOSKO). However, mitochondrial dysfunction in WT neurons occurs at lower concentrations of TNF-alpha when neurons are directly treated with TNF-alpha or co-cultured with TNF-alpha-treated microglia than iNOSKO neurons similarly treated. Immunofluorescent staining of primary neurons co-cultured with TNF-alpha-treated microglia reveals that the antioxidant enzyme in mitochondria, manganese superoxide dismutase (MnSOD), is co-localized with nitrotyrosine in WT but not in iNOSKO primary neuronal cells. Importantly, the percentage of surviving neurons is significantly reduced in WT neurons compared with iNOSKO neurons under identical treatment conditions. Together, the results suggest that TNF-alpha activates microglia to produce high levels of TNF-alpha and that production of nitric oxide (NO) in neurons is an important factor affecting MnSOD nitration and subsequent mitochondrial dysfunction.

Sperm lipid peroxidation and pro-inflammatory cytokines

AIM

To investigate if interleukin-6 (IL-6), interleukin-8 (IL-8), interleukin-10 (IL-10), interferon-gamma (IFN-gamma) or tumor necrosis factor-alpha (TNF-alpha) are able to stimulate the level of lipid peroxidation of sperm membranes, either alone or in the presence of leukocytes.

METHODS

Semen samples from normozoospermic donors were prepared by density gradient. The sperms were exposed to the indicated cytokines, at physiological and infection-inflammation concentrations, in the absence or presence of leukocytes. Lipid peroxidation of the sperm membranes was determined by measuring malondialdehyde (MDA) and 4-hydroxialkenals (HAE) formation.

RESULTS

TNF-alpha, IL-8 and IFN-gamma increased the level of sperm membrane lipid peroxidation when tested at physiological concentrations. At infection-inflammation concentrations, only IL-8 was able to produce a higher effect. When assayed in the presence of leucocytes, IL-8 and TNF-alpha showed a higher effect at infection-inflammation concentrations than at physiological concentrations. Finally, IL-8 showed a higher effect in the presence of leukocytes than in their absence at both physiological and infection-inflammation concentrations. TNF-alpha also showed a higher effect when assayed in the presence of leukocytes than in their absence, but only at infection-inflammation concentrations. There was no effect of IL-6 or IL-10 in any of the tested conditions.

CONCLUSION

Several pro-inflammatory cytokines at physiological concentrations increase the level of lipid peroxidation of sperm membranes, which could be important for the sperm fecundation process. However, infection-inflammation concentrations of some cytokines, such as IL-8 and TNF-alpha, either alone or in the presence of leukocytes, could drive the lipid peroxidation of the spermatozoa plasma membrane to levels that can affect the sperm fertility capacity.

Modulation of the age-related nuclear factor-kappaB (NF-kappaB) pathway by hesperetin

Nuclear factor-kappaB (NF-kappaB), a redox-sensitive transcription factor, plays an important role in the aging process. Thus, developing and identifying specific components that modulate NF-kappaB without adverse side-effects would be of major importance. Hesperetin, a flavanone abundant in citrus fruits, has a variety of pharmacological properties being antioxidant, cholesterol-lowering, and anti-inflammatory. In this study, we investigated how hesperetin fed to 6- and 24-month-old rats modulates NF-kappaB in their kidneys. Results showed that hesperetin suppressed NF-kappaB activation and related gene expressions. An even more interesting finding is that hesperetin suppressed NF-kappaB through four signal transduction pathways, NIK/IKK, ERK, p38, and JNK. Further evidence showed the remarkable efficacy of hesperetin to suppress the translocation of Trx/Ref-1, indicating its beneficial effect on the redox status. The most significant findings of the current study report new information on the use of hesperetin as a potential anti-aging agent.

Cross talk between nitric oxide and ERK1/2 signaling pathway in the spinal cord mediates naloxone-precipitated withdrawal in morphine-dependent rats

Our recent study has shown activation of spinal extracellular signal-regulated kinase-1 and -2 (ERK1/2), a member of the mitogen-activated protein kinase (MAPK) family, contributes to naloxone-precipitated withdrawal and withdrawal-induced spinal neuronal sensitization in morphine-dependent rats. However, the mechanism and significance of the spinal ERK1/2 activation during morphine dependence and withdrawal remain unknown. In this study, we reported that intrathecal (i.t.) pretreatment with either the non-selective nitric oxide synthase (NOS) inhibitor N(G)-nitro-L-arginine methyl ester (L-NAME), neuronal NOS (nNOS) inhibitor 7-nitro indazole (7-NI), or the inducible NOS (iNOS) inhibitor aminoguanidine (AG), could reduce morphine withdrawal-induced increase of phospho-ERK1/2 (pERK1/2) expression in the rat spinal cord. On the other hand, attenuation of the spinal ERK phosphorylation by the MAPK kinase (MEK) inhibitor U0126 also could inhibit the increase of nNOS and iNOS expression in the spinal cord of morphine withdrawal rats. Inhibitory expression of pERK1/2 by i.t. NOS inhibitor L-NAME, 7-NI or AG and of nNOS and iNOS by i.t. U0126 in the spinal cord were accompanied by decreased scores of morphine withdrawal and the inhibited spinal Fos protein (a maker for neuronal excitation or activation) expression induced by morphine withdrawal. These findings suggest cross talk between nitric oxide (NO) and the ERK1/2 signaling pathway mediates morphine withdrawal and withdrawal-induced spinal neuronal sensitization in morphine-dependent rats.

Contribution of inducible nitric oxide synthase and cyclooxygenase-2 to apoptosis induction in smooth chorion trophoblast cells of human fetal membrane tissues

We examined the contribution of apoptosis- and oxidative stress-associated genes to apoptosis induction in trophoblast cells of human fetal membrane tissues undergoing apoptosis during in vitro incubation. RT-PCR analyses demonstrated an increased level of HO-1, Mn-SOD, Cox-2, iNOS, TNFalpha, TNFR1, IL-1beta, IL-6, Bax, Bak, and Bad gene expression, while Bcl-2 mRNA expression level decreased. Western blot analyses demonstrated an increase in iNOS, Cox-2, and HO-1 protein levels; a decrease in pro-caspase-3 and 9, proform-PARP, and Apaf-1 protein levels; a leakage of cytochrome c from the mitochondria. An antioxidative reagent, general and selective Cox-2 inhibitors, and an iNOS inhibitor suppressed in vitro progression of the apoptosis. Furthermore, an NO donor reagent induced apoptosis in primary cultured trophoblast cells. Therefore, we concluded that the induction of apoptosis in the smooth chorion trophoblasts is mediated through oxidative stress induction followed by mitochondria damage, suggesting that iNOS and Cox-2 play an important role in the apoptosis induction in trophoblasts of human fetal membrane tissues.

Distinct signaling pathways for induction of type II NOS by IFNγ and LPS in BV-2 microglial cells

Nitric oxide (NO) release upon microglial cell activation has been implicated in the tissue injury and cell death in many neurodegenerative diseases. Recent studies have indicated the ability of interferon-gamma (IFNgamma) and lipopolysaccharides (LPS) to independently induce type II nitric oxide synthase (iNOS) expression and NO production in BV-2 microglial cells. However, a detailed comparison between the signaling pathways activating iNOS by these two agents has not been accomplished. Analysis of PKC isoforms revealed mainly the presence of PKCdelta, iota and lambda in BV-2 cells. Although both IFNgamma and LPS could specifically enhance the tyrosine phosphorylation of PKCdelta, treatment with IFNgamma induced a steady increase of phospho-PKCdelta for up to 1h, whereas treatment with LPS elevated phospho-PKCdelta levels only transiently, with peak activity at 5 min. Rottlerin, a specific inhibitor for PKCdelta, dose-dependently inhibited IFNgamma- and LPS-induced NO production. Despite the common involvement of PKCdelta, IFNgamma- but not LPS-induced NO production involved extracellular signal-regulated kinases (ERK1/2) cascade and IFNgamma-induced phosphorylation of ERK1/2 was mediated through PKC. On the other hand, LPS- but not IFNgamma-induced NO production was through stimulation of NF-kappaB activation and nuclear translocation to interact with DNA. These results demonstrated distinct signaling pathways for induction of iNOS by IFNgamma and LPS in BV-2 microglial cells.

Tristetraprolin regulates the expression of the human inducible nitric-oxide synthase gene

The expression of human inducible NO synthase (iNOS) is regulated both by transcriptional and post-transcriptional mechanisms. Stabilization of mRNAs often depends on activation of p38 mitogen-activated protein kinase (p38 MAPK). In human DLD-1 cells, inhibition of p38 MAPK by the compound 4-(4-fluorophenyl)-2-(4-methylsulfinylphenyl)-5-(4-pyridyl)1H-imidazole (SB203580) or by overexpression of a dominant-negative p38 MAPKalpha protein resulted in a reduction of human iNOS mRNA and protein expression, whereas human iNOS promoter activity was not affected. An important RNA binding protein regulated by the p38 MAPK pathway and involved in the regulation of the stability of several mRNAs is tristetraprolin. RNase protection, quantitative real-time polymerase chain reaction, and Western blot experiments showed that cytokines used to induce iNOS expression in DLD-1 cells also enhanced tristetraprolin expression. SB203580 incubation reduced cytokine-mediated enhancement of tristetraprolin expression. Overexpression or down-regulation of tristetraprolin in stably transfected DLD-1- or A549/8 cells consistently resulted in enhanced or reduced iNOS expression by modulating iNOS-mRNA stability. In UV cross-linking experiments, recombinant tristetraprolin did not interact with the human iNOS mRNA. However, coimmunoprecipitation experiments showed interaction of tristetraprolin with the KH-type splicing regulatory protein (KSRP), which is known to recruit mRNAs containing AU-rich elements to the exosome for degradation. This tristetraprolin-KSRP interaction was enhanced by cytokines and reduced by SB203580 treatment. We conclude that tristetraprolin positively regulates human iNOS expression by enhancing the stability of human iNOS mRNA. Because tristetraprolin does not directly bind to the human iNOS mRNA but interacts with KSRP, tristetraprolin is likely to stabilize iNOS mRNA by capturing the KSRP-exosome complex.

Recent advances in the regulation of nitric oxide in the kidney

Nitric oxide (NO) plays important roles in the regulation of renal function and the long-term control of blood pressure. New roles of NO have been proposed recently in diabetes, nephrotoxicity, and pregnancy. NO derived from all 3 NOS isoforms contributes to the overall regulation of kidney function, and recent advances in our understanding of their regulation have been made lately. In this regard, substrate and cofactor availability play important roles in regulating nitric oxide synthase (NOS) activity not only by limiting enzyme activity but also by influencing the coupling of NOS with its cofactors, tetrahydrobiopterin and NADPH. Protein-protein interactions are now recognized to be important negative and positive regulators of NOS. Phosphorylation is another component of the mechanism whereby NOS is activated or deactivated. Increased NOS expression can also influence enzyme activity; however, the degree of expression does not always correlate with enzyme activity because increased NO levels can result in inhibition of NOS. Finally, other potential regulators of NOS such as endogenous L-arginine analogs may also be important. In this article, we summarize recent advances in the regulation of activity and expression of the NOS isoforms within the kidney.

Vascular endothelial growth factor in diabetes induced early retinal abnormalities

Increased vascular permeability and blood flow alterations are characteristic features of diabetic retinal microangiopathy. The present study investigated vascular endothelial growth factor (VEGF) and its interactions with endothelin (ET) 1 and 3, endothelial, and inducible nitric oxide synthase (eNOS, iNOS) in mediating diabetes induced retinal vascular dysfunction. Male Sprague Dawley rats with streptozotocin (STZ) induced diabetes, with or without VEGF receptor signal inhibitor SU5416 treatment (high or low dose) were investigated after 4 weeks of follow-up. Colour Doppler ultrasound of the ophthalmic/central retinal artery, retinal tissue analysis with competitive RT-PCR and microvascular permeability were studied. Diabetes caused increased microvascular permeability along with increased VEGF mRNA expression. Increased vascular permeability was prevented by SU5416 treatment. Diabetic animals showed higher resistivity index (RI), indicative of vasoconstriction with increased ET-1 and ET-3 mRNA expression, whereas eNOS and iNOS mRNA expressions were un-affected. SU5416 treatment corrected increased RI via increased iNOS in spite of increased ET-1, ET-3 and VEGF mRNA expression. Cell culture (HUVEC) studies indicate that in part, an SU5416 induced iNOS upregulation may be mediated though a MAP kinase signalling pathway. The present data suggest VEGF is important in mediating both vasoconstriction and permeability in the retina in early diabetes.

Effects of pentoxifylline in adriamycin-induced renal disease in rats

Tumor necrosis factor-alpha (TNF-alpha) is a mediator of inflammation in human and animal renal disease. Pentoxiphylline (PTX) is an inhibitor of TNF-alpha. In this study we examined the effects of PTX on TNF-alpha, proteinuria, nitrite production, and apoptosis in an experimental model of Adriamycin (ADR) nephropathy in rats. Rats were divided into four groups: untreated Wistar rats (controls), PTX treatment alone, ADR treatment alone to induce nephropathy, and ADR treatment followed by PTX. ADR treatment followed by PTX treatment prevented the increase in serum TNF-alpha levels and proteinuria in rats with ADR-nephropathy ( P<0.05). Urine nitrite levels were significantly increased in the ADR-induced nephropathy group and the increase was prevented in the ADR-induced nephropathy group when they also received PTX. The urine nitrite levels were not different between the PTX-treated group and the untreated control rats. PTX prevented the rise of serum TNF-alpha in ADR nephropathy rats and a decrease in proteinuria, urine nitrite, and apoptosis in the renal tissue. These findings suggest a beneficial anti-inflammatory effect of PTX.

Retinal ischemia: mechanisms of damage and potential therapeutic strategies

Retinal ischemia is a common cause of visual impairment and blindness. At the cellular level, ischemic retinal injury consists of a self-reinforcing destructive cascade involving neuronal depolarisation, calcium influx and oxidative stress initiated by energy failure and increased glutamatergic stimulation. There is a cell-specific sensitivity to ischemic injury which may reflect variability in the balance of excitatory and inhibitory neurotransmitter receptors on a given cell. A number of animal models and analytical techniques have been used to study retinal ischemia, and an increasing number of treatments have been shown to interrupt the "ischemic cascade" and attenuate the detrimental effects of retinal ischemia. Thus far, however, success in the laboratory has not been translated to the clinic. Difficulties with the route of administration, dosage, and adverse effects may render certain experimental treatments clinically unusable. Furthermore, neuroprotection-based treatment strategies for stroke have so far been disappointing. However, compared to the brain, the retina exhibits a remarkable natural resistance to ischemic injury, which may reflect its peculiar metabolism and unique environment. Given the increasing understanding of the events involved in ischemic neuronal injury it is hoped that clinically effective treatments for retinal ischemia will soon be available.

Pyrrolidine dithiocarbamate reduces renal dysfunction and injury caused by ischemia/reperfusion of the rat kidney

Dithiocarbamates can modulate the expression of genes associated with inflammation or development of ischemia/reperfusion injury. Here, we investigate the effects of pyrrolidine dithiocarbamate, an inhibitor of nuclear factor (NF)-kappaB activation, on the renal dysfunction and injury caused by ischemia/reperfusion of the rat kidney. Bilateral clamping of renal pedicles (45 min) followed by reperfusion (6 h) caused significant renal dysfunction and marked renal injury. Pyrrolidine dithiocarbamate (100 mg/kg, administered i.v.) significantly reduced biochemical and histological evidence of renal dysfunction and injury caused by ischemia/reperfusion of the rat kidney. Furthermore, pyrrolidine dithiocarbamate markedly reduced the expression of inducible nitric oxide synthase (iNOS) protein and significantly reduced serum levels of nitric oxide. Finally, pyrrolidine dithiocarbamate inhibited the activation of NF-kappaB by preventing its translocation from the cytoplasm into the nuclei of renal cells. These results demonstrate that pyrrolidine dithiocarbamate reduces renal ischemia/reperfusion injury and that dithiocarbamates may provide beneficial actions against ischemic acute renal failure.