NF-kappa B activation by oxidative stress and inflammation suppresses contractility in colonic circular smooth muscle cells

Resuscitation-induced intestinal edema and related dysfunction: state of the science

High volume resuscitation and damage control surgical methods, while responsible for significantly decreasing morbidity and mortality from traumatic injuries, are associated with pathophysiologic derangements that lead to subsequent end organ edema and dysfunction. Alterations in hydrostatic and oncotic pressures frequently result in intestinal edema and subsequent dysfunction. The purpose of this review is to examine the principles involved in the development of intestinal edema, current and historical models for the study of edema, effects of edema on intestinal function (particularly ileus), molecular mediators governing edema-induced dysfunction, potential role of mechanotransduction , and therapeutic effects of hypertonic saline. We review the current state of the science as it relates to resuscitation induced intestinal edema and resultant dysfunction.

Role of hydrogen peroxide in NF-kappaB activation: from inducer to modulator

Hydrogen peroxide (H2O2) has been implicated in the regulation of the transcription factor NF-kappaB, a key regulator of the inflammatory process and adaptive immunity. However, no consensus exists regarding the regulatory role played by H2O2. We discuss how the experimental methodologies used to expose cells to H2O2 produce inconsistent results that are difficult to compare, and how the steady-state titration with H2O2 emerges as an adequate tool to overcome these problems. The redox targets of H2O2 in the NF-kappaB pathway--from the membrane to the post-translational modifications in both NF-kappaB and histones in the nucleus--are described. We also review how H2O2 acts as a specific regulator at the level of the single gene, and briefly discuss the implications of this regulation for human health in the context of kappaB polymorphisms. In conclusion, after near 30 years of research, H2O2 emerges not as an inducer of NF-kappaB, but as an agent able to modulate the activation of the NF-kappaB pathway by other agents. This modulation is generic at the level of the whole pathway but specific at the level of the single gene. Therefore, H2O2 is a fine-tuning regulator of NF-kappaB-dependent processes, as exemplified by its dual regulation of inflammation.

Activation of nuclear factor-kappaB in dogs with chronic enteropathies

Homeostasis in the intestinal microenvironment between the immune system and luminal antigens appears disturbed in chronic enteropathies. Pro-inflammatory cytokines likely play a role in the pathogenesis of intestinal inflammation. Several inflammatory and immunoregulatory genes have associated nuclear factor-kappaB (NF-kappaB) binding sites, which allow NF-kappaB to regulate gene transcription. The purpose of this study was to investigate (1) the occurrence of NF-kappaB activation during mucosal inflammation in situ, (2) the mucosal distribution pattern of cells expressing activated NF-kappaB within treatment groups, and (3) the effect of specific therapy on NF-kappaB activation. Dogs with chronic enteropathy were studied (n=26) and compared with 13 healthy dogs. Ten dogs had food responsive disease (FRD) and 16 had inflammatory bowel disease (IBD). NF-kappaB activation was detected in duodenal mucosal biopsies using a mouse monoclonal antibody (MAB 3026) that selectively binds the nuclear localization sequence of activated NF-kappaB. To identify macrophages, biopsies were stained using the MAC 387 antibody. Macrophages in the lamina propria double-stained for MAC 387 and NF-kappaB were quantitated; epithelial cell expression of activated NF-kappaB was determined semi-quantitatively. Results showed that more macrophages positive for activated NF-kappaB were present in lamina propria of dogs with chronic enteropathy compared to control dogs (p<0.01). More NF-kappaB positive epithelial cells were observed in FRD dogs compared to IBD dogs (p<0.05). After therapy, the number of macrophages and epithelial cells staining positive for activated NF-kappaB decreased (p<0.01) in chronic enteropathy dogs. In conclusion, activation of NF-kappaB is closely associated with the pathophysiology of canine chronic enteropathy. Down-regulation follows successful therapy.

Suppressive effect of an isoflavone fraction on tumor necrosis factor-alpha-induced interleukin-8 production in human intestinal epithelial Caco-2 cells

This study demonstrates the effect of soybean components on the tumor necrosis factor-alpha (TNF-alpha)-induced production of interleukin-8 (IL-8), one of the major inflammatory chemokines, in intestinal epithelial-like Caco-2 cells. Among the soybean components, an isoflavone fraction (IFF) suppressed the TNF-alpha-induced IL-8 secretion by Caco-2 cells in a dose-dependent manner, whereas a soyasaponin fraction and soypeptide fraction had no significant effect on TNF-alpha-induced IL-8 secretion. The IL-8 secretion induced by hydrogen peroxide and by IL-1beta was not suppressed by IFF, suggesting that the inhibitory effect of isoflavone was specific for the TNF-alpha-induced regulation of IL-8. The increased expression of IL-8 mRNA by TNF-alpha was almost completely suppressed by IFF. Furthermore, the transcriptional activity of the human IL-8 promoter was increased by the TNF-alpha treatment, and IFF significantly suppressed the IL-8 promoter activity. These results indicate that IFF suppressed TNF-alpha-induced IL-8 production at the transcriptional level in human intestinal Caco-2 cells, suggesting IFF of soybean as a promising food component for preventing intestinal inflammation such as inflammatory bowel disease.

Gene therapy of Cav1.2 channel with VIP and VIP receptor agonists and antagonists: a novel approach to designing promotility and antimotility agents

Recent findings show that the enteric neurotransmitter VIP enhances gene transcription of the alpha1C subunit of Cav1.2 (L-type) Ca2+ channels in the primary cultures of human colonic circular smooth muscle cells and circular smooth muscle strips. In this study, we investigated whether systemic infusion of VIP in intact animals enhances the gene transcription and protein expression of these channels to accelerate colonic transit. We also investigated whether similar systemic infusions of VPAC1/2 receptor antagonist retards colonic transit by repressing the constitutive gene expression of the alpha1C subunit. We found that the systemic infusion of VIP for 7 days by a surgically implanted osmotic pump enhances the gene and protein expression of the alpha1C subunit and circular muscle contractility in the proximal and the middle rat colons, but not in the distal colon. A similar systemic infusion of VPAC1/2 receptor antagonist represses the expression of the alpha1C subunit and circular smooth muscle contractility in the proximal and the middle colons. The VIP infusion accelerates colonic transit and pellet defecation by rats, whereas the infusion of VPAC1/2 receptor antagonist retards colonic transit and pellet defecation. VPAC1 receptors, but not VPAC2 receptors, mediate the above gene transcription-induced promotility effects of VIP. We conclude that VIP and VPAC(1) receptor agonists may serve as potential promotility agents in constipation-like conditions, whereas VPAC receptor antagonists may serve as potential antimotility agents in diarrhea-like conditions produced by enhanced motility function.

Interleukin-1beta up-regulates RGS4 through the canonical IKK2/IkappaBalpha/NF-kappaB pathway in rabbit colonic smooth muscle

Initial Ca2+-dependent contraction of the intestinal smooth muscle mediated by G(q)-coupled receptors is attenuated by RGS4 (regulator of G-protein signalling 4). Treatment of colonic muscle cells with IL-1beta (interleukin-1beta) inhibits acetylcholine-stimulated initial contraction through increasing the expression of RGS4. NF-kappaB (nuclear factor kappaB) signalling is the dominant pathway activated by IL-1beta. In the present study we show that RGS4 is a new target gene regulated by IL-1beta/NF-kappaB signalling. Exposure of cultured rabbit colonic muscle cells to IL-1beta induced a rapid increase in RGS4 mRNA expression, which was abolished by pretreatment with a transcription inhibitor, actinomycin D, implying a transcription-dependent mechanism. Existence of the canonical IKK2 [IkappaB (inhibitor of NF-kappaB) kinase 2]/IkappaBalpha pathway of NF-kappaB activation induced by IL-1beta in rabbit colonic muscle cells was validated with multiple approaches, including the induction of reporter luciferase activity and endogenous NF-kappaB-target gene expression, NF-kappaB-DNA binding activity, p65 nuclear translocation, IkappaBalpha degradation and the phosphorylation of IKK2 at Ser(177/181) and p65 at Ser(536). RGS4 up-regulation by IL-1beta was blocked by selective inhibitors of IKK2, IkappaBalpha or NF-kappaB activation, by effective siRNA (small interfering RNA) of IKK2, and in cells expressing either the kinase-inactive IKK2 mutant (K44A) or the phosphorylation-deficient IkappaBalpha mutant (S32A/S36A). An IKK2-specific inhibitor or effective siRNA prevented IL-1beta-induced inhibition of acetylcholine-stimulated PLC-beta (phopsholipase C-beta) activation. These results suggest that the canonical IKK2/IkappaBalpha pathway of NF-kappaB activation mediates the up-regulation of RGS4 expression in response to IL-1beta and contributes to the inhibitory effect of IL-1beta on acetylcholine-stimulated PLC-beta-dependent initial contraction in rabbit colonic smooth muscle.

Potential contribution of nuclear factor-kappaB to cerebral vasospasm after experimental subarachnoid hemorrhage in rabbits

Nuclear factor-kappaB (NF-kappaB) plays a key role in inflammation, which is involved in the development of cerebral vasospasm after subarachnoid hemorrhage (SAH). In the present study, we assessed the potential role of NF-kappaB in regulation of cerebral vasospasm. Nuclear factor-kappaB DNA-binding activity was measured in cultured vascular smooth muscle cells (VSMCs) treated with hemolysate and pyrrolidine dithiocarbamate (PDTC, 80 micromol/L), an inhibitor of NF-kappaB. Forty-two rabbits were divided into three groups: control, SAH, and PDTC groups (n=14 for each group). The caliber of the basilar artery was evaluated. Nuclear factor-kappaB DNA-binding activity and the gene expression levels of cytokines and adhesion molecules in the basilar artery were measured. Immunohistochemical study was performed to assess the expression and localization of tumor necrosis factor (TNF)-alpha, intercellular adhesion molecule (ICAM)-1, and myeloperoxidase (MPO). It was observed that NF-kappaB DNA-binding activity was significantly increased by treatment with hemolysate in cultured VSCMs, but this increase was suppressed by pretreatment with PDTC. Severe vasospasm was observed in the SAH group, which was attenuated in the PDTC group. Subarachnoid hemorrhage could induce increases of NF-kappaB DNA-binding activity and the gene expression levels of TNF-alpha, interleukin (IL)-1 beta, ICAM-1, and vascular cell adhesion molecule (VCAM)-1, which were reduced in the PDTC group. Immunohistochemical study demonstrated that the expression levels of TNF-alpha, ICAM-1, and MPO were all increased in the SAH group, but these increases were attenuated in the PDTC group. Our results suggest that NF-kappaB is activated in the arterial wall after SAH, which potentially leads to vasospasm development through induction of inflammatory response.

Induction of colitis causes inflammatory responses in fat depots: evidence for substance P pathways in human mesenteric preadipocytes

Intracolonic administration of trinitrobenzene sulfonic acid in mice causes inflammation in the colon that is accompanied by increased expression of proinflammatory cytokines and of the substance P (SP), neurokinin 1 receptor (NK-1R) in the proximal mesenteric fat depot. We also investigated whether human mesenteric preadipocytes contain NK-1R and examined the functional consequences of exposure of these cells to SP as it relates to proinflammatory signaling. We found that human mesenteric preadipocytes express NK-1R both at the mRNA and protein levels. Exposure of human mesenteric preadipocytes to SP increased NK-1R mRNA and protein expression by 3-fold, and stimulated IL-8 mRNA expression and protein secretion. This effect was abolished when these cells were pretreated with the specific NK-1R antagonist CJ 012,255. Moreover, human mesenteric preadipocytes transfected with a luciferase promoter/reporter system containing the IL-8 promoter with a mutated NF-kappaB site lost their ability to respond to SP, indicating that SP-induced IL-8 expression is NF-kappaB-dependent. This report indicates that human mesenteric preadipocytes contain functional SP receptors that are linked to proinflammatory pathways, and that SP can directly increase NK-1R expression. We speculate that mesenteric fat depots may participate in intestinal inflammatory responses via SP-NK-1R-related pathways, as well as other systemic responses to the presence of an ongoing inflammation of the colon.

Negative transcriptional regulation of human colonic smooth muscle Cav1.2 channels by p50 and p65 subunits of nuclear factor-kappaB

BACKGROUND & AIMS

The expression of Cav1.2 channels in colonic circular smooth muscle cells and the contractility of these cells are suppressed in inflammation. Our aim was to investigate whether the activation of p50 and p65 nuclear factor-kappaB subunits mediates these effects.

METHODS

Primary cultures of human colonic circular smooth muscle cells and muscle strips were used.

RESULTS

The messenger RNA and protein expression of the pore-forming alpha1C subunit of Cav1.2 channels decreased time dependently in response to tumor necrosis factor alpha. This effect was blocked by prior transient transfection of the cells with antisense oligonucleotides to p50 or p65. The overexpression of p50 and p65 inhibited the constitutive expression of alpha1C. Three putative kappaB binding motifs were identified on the 5' flanking region of exon 1b of the human L-type calcium channel alpha1C gene. Progressive 5' deletions of the promoter and point mutations of the kappaB binding motifs indicated that the two 5' binding sites, but not the third 3' binding site, were essential for the suppression of alpha1C. Transient transfection of human colonic circular muscle strips with antisense oligonucleotides to p50 and p65 decreased expression of the 2 nuclear factor-kappaB units and reversed the suppression of alpha1C, as well as that of the contractile response to acetylcholine, by 24 hours of treatment with tumor necrosis factor alpha.

CONCLUSIONS

The activation of p50 and p65 by tumor necrosis factor alpha suppresses the expression of the alpha1C subunit of Cav1.2 channels in human colonic circular smooth muscle cells and their contractile response to acetylcholine. Nuclear factor-kappaB must bind concurrently to the two 5' kappaB motifs on the promoter of alpha1C to produce this effect.

Transcriptional regulation of inflammatory mediators secreted by human colonic circular smooth muscle cells

We investigated the transcriptional regulation of secretion of pro- and anti-inflammatory mediators by human colonic circular smooth muscle cells (HCCSMC) in response to tumor necrosis factor (TNF)-alpha. Gene chip array analysis indicated that HCCSMC express a specific panel of 11 cytokines, chemokines, and cell adhesion molecules in a time-dependent manner in response to TNF-alpha. The chip array data were supported by quantitative analysis of mRNA and protein expressions of interleukin (IL)-6, IL-8, intercellular adhesion molecule (ICAM)-1 and IL-11. The proinflammatory mediators were expressed early, whereas the anti-inflammatory cytokine IL-11 was expressed late after TNF-alpha treatment. The expression of ICAM-1 on HCCSMC increased lymphocyte adhesion to these cells, which was blocked by pretreatment with antibody to ICAM-1. TNF-alpha acted on both R(1) and R(2) receptors to induce the expression of ICAM-1. Pretreatment of HCCSMC with antisense oligonucleotides to p65 nuclear factor-kappaB (NF-kappaB) blocked the expression of ICAM-1, whereas pretreatment with antisense oligonucleotides to p50 NF-kappaB had little effect. The overexpression of p65 NF-kappaB enhanced the constitutive expression of ICAM-1, and TNF-alpha treatment had no further effect. The delayed expression of endogenous IL-11 limited the expression of ICAM-1, and pretreatment of HCCSMC with antisense oligonucleotides to IL-11 enhanced it. We conclude that TNF-alpha induces gene expression in HCCSMC for programmed synthesis and release of pro- and anti-inflammatory mediators.

Expression of multiple CaV1.2 transcripts in rat tissues mediated by different promoters

The expression of two different transcripts for Ca(V)1.2 in rat tissues mirrors that which has previously been described for human tissue, in that expression of transcripts expressing exon 1a is predominant only in heart, whereas expression of transcripts expressing exon 1b is greater in smooth muscle rich tissues such as aorta and intestine. Transcripts expressing exon 1b also predominate in brain and in diaphragm. Western blots indicate that the N-terminus coded for by exon 1b is present in much of the protein in all these tissues except heart. The promoter just upstream of exon 1b has been cloned, sequenced and utilized to drive expression of luciferase in smooth muscle A7r5 cells, cardiac HL-1 cells, skeletal muscle L6 cells and neuronal PC12 cells. The nucleotide sequence of the promoter exhibits 80% identity with the equivalent promoter previously identified in humans and 94% identity with the sequence of the equivalent region of the mouse genome. Evidence in favor of still another promoter upstream of exon 2 has been uncovered.

TNFalpha suppresses human colonic circular smooth muscle cell contractility by SP1- and NF-kappaB-mediated induction of ICAM-1

BACKGROUND & AIMS

Intercellular adhesion molecule 1 (ICAM-1) receptors are expressed at low levels on human colonic circular smooth muscle cells (HCCSMCs) and their expression is increased in patients with Crohn's disease. We investigated the roles of transcription factors Sp1 and nuclear factor kappa B (NF-kappaB) in the regulation of ICAM-1 expression on HCCSMCs and examined whether ICAM-1 expression mediates the suppression of contractility in response to TNFalpha.

METHODS

Experiments were performed on primary cultures of HCCSMCs and fresh human colonic circular muscle strips.

RESULTS

TNFalpha treatment of HCCSMCs induced rapid and prolonged accumulation of ICAM-1 messenger RNA (mRNA) and protein. NF-kappaB inhibition before, but not after, 1 hour of TNFalpha-stimulation blocked the expression of ICAM-1. TNFalpha significantly enhanced Sp1/DNA binding. Sp1 bound to the 3' flanking region of a variant kappaB site in the -192/-172 region of ICAM-1 promoter. Mutation of this region abolished the response to TNFalpha. The treatment of HCCSMCs with Sp1 antisense oligonucleotides (ODNs) blocked the expression of ICAM-1, but sense ODNs had no effect. Protein kinase C zeta (PKCzeta) inhibition before or 3 hours after stimulation with TNFalpha also blocked the expression of ICAM-1. TNFalpha treatment of circular muscle strips pretreated with ICAM-1 sense ODNs or control medium significantly reduced their response to acetylcholine, whereas pretreatment with antisense ODNs blocked this effect.

CONCLUSIONS

The expression of ICAM-1 on HCCSMCs in response to TNFalpha is regulated by transcription factors Sp1 and NF-kappaB binding independently to the -192/-172 region of the ICAM-1 promoter. The expression of ICAM-1 plays a critical role in the suppression of cell contractility in response to TNFalpha.

Roles of NF-kappaB and SP-1 in oxidative stress-mediated induction of platelet-derived growth factor-B by TNFalpha in human endothelial cells

Platelet-derived growth factor-B (PDGF-B) is upregulated by proinflamatory stimuli in the early stages of atherosclerosis. However, its mechanisms are not fully elucidated. In the present study, by using the antioxidant N-acetylcysteine (NAC), we investigated in human umbilical vein endothelial cells (HUVECs) the roles of oxidative stress in PDGF-B expression induced by tumor necrosis factor alpha (TNFalpha) and its underlying mechanisms. Exposure of HUVECs to TNFalpha (200 U/ml) for 24 hours caused significant increases of both the PDGF-B expression and its promoter/enhancer activity, which were abolished by NAC (20 mmol/L). Accordingly, a prolonged oxidative stress was induced by TNFalpha and that was prevented by pretreatment with NAC. Electrophoresis mobility shift assay (EMSA) and Western blot analysis showed that both the nuclear factor-kappaB (NF-kappaB) and the specificity protein-1 (SP-1) were activated by TNFalpha. However, NAC only partially inhibited the TNFalpha-induced activation of NF-kappaB, but abolished the activation of SP-1. Mutation of the NF-kappaB binding site resulted in a moderate reduction in the TNFalpha-induced activity of PDGF-B promoter/enhancer, whereas mutation of SP-1 binding site resulted in an absence of induction by TNFalpha. These results suggest that oxidative stress mediates the TNFalpha-induced expression of PDGF-B in HUVECs through redox-sensitive transcription factors, predominantly the SP-1 and possibly, to some extent of NF-kappaB.

Hydrogen peroxide in the Burkitt's lymphoma cell line Raji provides protection against arsenic trioxide-induced apoptosis via the phosphoinositide-3 kinase signalling pathway

Many anticarcinogenic drugs kill tumour cells by inducing apoptosis. We examined the effects of hydrogen peroxide (H(2)O(2)) on arsenic trioxide (As(2)O(3))-induced cell killing. Low concentrations of H(2)O(2) (200 micromol/l) inhibited the ability of As(2)O(3) to induce apoptosis in the Burkitt's lymphoma cell line Raji. H(2)O(2) altered the form of cell death from apoptosis to pyknosis/necrosis and also lowered the degree of cell killing by As(2)O(3). H(2)O(2) was capable of preventing caspase-3 activation induced by As(2)O(3) in Raji cells. Incubation of cells with a phosphoinositide-3 kinase (PI-3K) inhibitor, wortmannin (100 nmol/l), blocked the effects of H(2)O(2) on As(2)O(3)-induced caspase-3 activation. In addition, the PI-3K inhibitor partially blocked the effects of H(2)O(2) on up-regulation of Bcl-2 and Bcl-X(L) protein expression, down-regulation of Bax protein expression, and phosphorylation of Bcl-2 and IkappaBalpha. This investigation demonstrated for the first time that low concentrations of H(2)O(2) provide protection against the in vivo of As(2)O(3)-induced apoptosis. PI-3K plays a crucial role in enhancing cell survival during H(2)O(2), inhibiting As(2)O(3)-induced apoptosis in the Burkitt's lymphoma cells. As(2)O(3)-induced cancer cell apoptosis may be enhanced by certain antioxidants in the treatment protocol.

Update in inflammatory bowel disease pathogenesis

PURPOSE OF REVIEW

During the last few years, significant advances have been achieved in the understanding of the pathogenesis of inflammatory bowel disease (IBD). By gaining new insights, paradigms that seemed to be a safe basis of our knowledge on IBD pathogenesis have recently become doubtful. This review discusses and summarizes the most recent developments.

RECENT FINDINGS

Important new insights have been gained into the function of caspase-activating and recruitment domain-15 (CARD15)/NOD2, the first cloned susceptibility gene for Crohn disease (CD). New data on CARD15/NOD2 function and nuclear factor-kappaB activation indicate that an inflammatory reaction of the intestinal mucosa as a response of the innate immune system may be necessary for the maintenance of gut homeostasis. CD may therefore be seen as a defective immune response, no longer only as hyperresponsiveness of the mucosal immune system. Data on CARD15/NOD2 expression suggest that macrophages and epithelial cells could be the site of a primary pathophysiologic defect, and T-cell activation might just be a secondary effect inducing chronification of the inflammation, perhaps as a backup mechanism to a defective innate immunity. In addition to CARD15/NOD2, there are additional "innate" pathways by which commensal and pathogenic bacteria can directly interact with cells of the intestinal mucosa (eg, toll-like receptors). The "germ concept" and the "genetic concept" of IBD pathophysiology are converging.

SUMMARY

New findings are changing our concepts of the pathogenesis of IBD. The innate immune system, early responses to bacterial products, and the modulation of T-cell responses are important aspects that are reviewed.

Novel effect of NF-kappaB activation: carbonylation and nitration injury to cytoskeleton and disruption of monolayer barrier in intestinal epithelium

Using monolayers of intestinal cells, we reported that upregulation of inducible nitric oxide synthase (iNOS) is required for oxidative injury and that activation of NF-kappaB is key to cytoskeletal instability. In the present study, we hypothesized that NF-kappaB activation is crucial to oxidant-induced iNOS upregulation and its injurious consequences: cytoskeletal oxidation and nitration and monolayer dysfunction. Wild-type (WT) cells were pretreated with inhibitors of NF-kappaB, with or without exposure to oxidant (H(2)O(2)). Other cells were transfected with an IkappaBalpha mutant (an inhibitor of NF-kappaB). Relative to WT cells exposed to vehicle, oxidant exposure caused increases in IkappaBalpha instability, NF-kappaB subunit activation, iNOS-related activity (NO, oxidative stress, tubulin nitration), microtubule disassembly and instability (increased monomeric and decreased polymeric tubulin), and monolayer disruption. Monolayers pretreated with NF-kappaB inhibitors (MG-132, lactacystin) were protected against oxidation, showing decreases in all measures of the NF-kappaB --> iNOS --> NO pathway. Dominant mutant stabilization of IkappaBalpha to inactivate NF-kappaB suppressed all measures of the iNOS/NO upregulation while protecting monolayers against oxidant insult. In these mutants, we found prevention of tubulin nitration and oxidation and enhancement of cytoskeletal and monolayer stability. We concluded that 1) NF-kappaB is required for oxidant-induced iNOS upregulation and for the consequent nitration and oxidation of cytoskeleton; 2) NF-kappaB activation causes cytoskeletal injury following upregulation of NO-driven processes; and 3) the molecular event underlying the destabilizing effects of NF-kappaB appears to be increases in carbonylation and nitrotyrosination of the subunit components of cytoskeleton. The ability to promote NO overproduction and cytoskeletal nitration/oxidation is a novel mechanism not previously attributed to NF-kappaB in cells.

Inhibition of oxidant-induced nuclear factor-kappaB activation and inhibitory-kappaBalpha degradation and instability of F-actin cytoskeletal dynamics and barrier function by epidermal growth factor: key role of phospholipase-gamma isoform

Using monolayers of intestinal (Caco-2) cells as a model for studying inflammatory bowel disease (IBD), we previously showed that nuclear factor-kappaB (NF-kappaB) activation is required for oxidant-induced disruption of cytoskeletal and barrier integrity. Epidermal growth factor (EGF) stabilizes the F-actin cytoskeleton and protects against oxidant damage, but the mechanism remains unclear. We hypothesized that the mechanism involves activation of phospholipase C-gamma (PLC-gamma), which prevents NF-kappaB activation and the consequences of this activation, namely, cytoskeletal and barrier disruption. We studied wild-type and transfected cells. The latter were transfected with varying levels (1-5 microg) of cDNA to either stably overexpress PLC-gamma or to inhibit its activation. Cells were pretreated with EGF before exposure to oxidant (H(2)O(2)). Stably overexpressing PLC-gamma (+2.0-fold) or preincubating with EGF protected against oxidant injury as indicated by 1) decreases in several NF-kappaB-related variables [NF-kappaB (p50/p65 subunit) nuclear translocation, NF-kappaB subunit activity, inhibitory-kappaBalpha (I-kappaBalpha) phosphorylation and degradation]; 2) increases in F-actin and decreases in G-actin; 3) stabilization of the actin cytoskeletal architecture; and 4) enhancement of barrier function. Overexpression induced inactivation of NF-kappaB was potentiated by EGF. PLC-gamma was found mostly in membrane and cytoskeletal fractions (<9% in the cytosolic fractions), indicating its activation. Dominant negative inhibition of endogenous PLC-gamma (-99%) substantially prevented all measures of EGF protection against NF-kappaB activation. We concluded 1) EGF protects against oxidant-induced barrier disruption through PLC-gamma activation, which inactivates NF-kappaB; 2) Activation of PLC-gamma by itself is protective against NF-kappaB activation; 3) the ability to modulate the dynamics of NF-kappaB/I-kappa Balpha is a novel mechanism not previously attributed to the PLC family of isoforms in cells; and 4) development of PLC-gamma mimetics represents a possible new therapeutic strategy for IBD.

Ameliorative effects of sodium ferulate on experimental colitis and their mechanisms in rats

AIM: To investigate the ameliorative effects of sodium ferulate (SF) on acetic acid-induced colitis and their mechanisms in rats.

METHODS: The colitis model of Sprague-Dawley rats was induced by intracolon enema with 8% (V/V) of acetic acid. The experimental animals were randomly divided into model control, 5-aminosalicylic acid therapy group and three dose of SF therapy groups. The 5 groups were treated intracolonically with normal saline, 5-aminosalicylic acid (100 mg•kg^-1), and SF at the doses of 200, 400 and 800 mg·kg^-1 respectively and daily (8: 00 am) for 7 d 24 h following the induction of colitis. A normal control group of rats clystered with normal saline instead of acetic acid was also included in the study. Pathological changes of the colonic mucosa were evaluated by the colon mucosa damage index (CMDI) and the histopathological score (HS). The insulted colonic mucosa was sampled for a variety of determinations at the end of experiment when the animals were sacrificed by decapitation. Colonic activities of myeloperoxidase (MPO) and superoxide dismutase (SOD), and levels of malondialdehyde (MDA) and nitric oxide (NO) were assayed with ultraviolet spectrophotometry. Colonic contents of prostaglandin E2 (PGE2) and thromboxane B2 (TXB2) were determined by radioimmunoassay. The expressions of inducible nitric oxide synthase (iNOS), cyclo-oxygenase-2 (COX-2) and nuclear factor kappa B (NF-κB) p65 proteins in the colonic tissue were detected with immunohistochemistry.

RESULTS: Enhanced colonic mucosal injury, inflammatory response and oxidative stress were observed in the animals clystered with acetic acid, which manifested as the significant increase of CMDI, HS, MPO activities, MDA and NO levels, PGE₂ and TXB₂ contents, as well as the expressions of iNOS, COX-2 and NF-κB p65 proteins in the colonic mucosa, although the colonic SOD activity was significantly decreased compared with the normal control (CMDI: 2.9 ± 0.6 vs 0.0 ± 0.0; HS: 4.3 ± 0.9 vs 0.7 ± 1.1; MPO: 98.1 ± 26.9 vs 24.8 ± 11.5; MDA: 57.53 ± 12.36 vs 9.21 ± 3.85; NO: 0.331 ± 0.092 vs 0.176 ± 0.045; PGE₂: 186.2 ± 96.2 vs 42.8 ± 32.8; TXB₂: 34.26 ± 13.51 vs 8.83 ± 3.75; iNOS: 0.365 ± 0.026 vs 0.053 ± 0.015; COX-2: 0.296 ± 0.028 vs 0.034 ± 0.013; NF-κB p65: 0.314 ± 0.026 vs 0.039 ± 0.012; SOD: 28.33 ± 1.17 vs 36.14 ± 1.91; P < 0.01). However, these parameters were found to be significantly ameliorated in rats treated locally with SF at the given dose protocols, especially at 400 mg·kg^-1 and 800 mg·kg^-1 doses (CMDI: 1.8 ± 0.8, 1.6 ± 0.9; HS: 3.3 ± 0.9, 3.1 ± 1.0; MPO: 63.8 ± 30.5, 36.2 ± 14.2; MDA: 41.84 ± 10.62, 37.34 ± 8.58; NO: 0.247 ± 0.042; 0.216 ± 0.033; PGE₂: 77.2 ± 26.9, 58.4 ± 23.9; TXB₂: 18.07 ± 14.83; 15.52 ± 8.62; iNOS:0.175 ± 0.018, 0.106 ± 0.019; COX-2: 0.064 ± 0.018, 0.056 ± 0.014; NF-κBp65: 0.215 ± 0.019, 0.189 ± 0.016; SOD: 32.15 ± 4.26, 33.24 ± 3.69; P < 0.05-0.01). Moreover, a therapeutic dose protocol of 800 mg·kg^-1 SF was observed as effective as 100 mg·kg^-1 of 5-ASA in the amelioration of colonic mucosal injury as evaluated by CMDI and HS.

CONCLUSION: Administration of SF intracolonically may have significant therapeutic effects on the rat model of colitis induced by acetic acid enema, which was probably due to the mechanism of antioxidation, inhibition of arachidonic acid metabolism and NF-κB expression.