Review article: the potential role of nitric oxide in chronic inflammatory bowel disorders

Can glucose-insulin-potassium regimen suppress inflammatory bowel disease?

Insulin seems to have the ability to suppress the production of tumor necrosis factor-alpha and superoxide anion, enhance the synthesis of nitric oxide and inhibit the expression of intercellular adhesion molecule-1 (ICAM-1) through stimulation of nitric oxide. This suggests that insulin can behave as an anti-inflammatory molecule. In view of this, it is suggested that insulin in combination with glucose and potassium may be of benefit in the management of inflammatory bowel disease.

Hyperhomocysteinemia and inflammatory bowel disease: prevalence and predictors in a cross-sectional study

OBJECTIVE

Homocysteine is a sulfur-containing amino acid formed during the demethylation of methionine. Vitamin B12 and folate deficiency and therapy with antifolate drugs may predispose patients with inflammatory bowel disease (IBD) to hyperhomocysteinemia. The known associations between hyperhomocysteinemia and smoking, osteoporosis, and thrombosis make it an interesting candidate as a pathogenetic link in IBD. The aim of this study was to identify the prevalence and risk factors of hyperhomocysteinemia in patients with IBD.

METHODS

Sixty-five consecutive IBD patients were recruited from a tertiary outpatient gastroenterology practice. Fasting plasma homocysteine levels were measured, along with vitamin B12 and folate. Data regarding medication use, multivitamin use, disease location and severity, and extraintestinal manifestations of IBD were gathered. Homocysteine levels in 138 healthy control subjects were compared with the IBD cohort, and adjustments for age and sex were made using logistic regression. Multivariate analysis was performed to seek predictors of homocysteine levels.

RESULTS

The mean age in the IBD cohort was 42+/-13.4 yr (+/-SD), and 43% were male. The mean disease duration was 13.8+/-9.4 yr, and 32% had used steroids within the last 3 months. Immunomodulator therapy had been used in 32%, and 75% had had an intestinal resection. Osteoporosis was present in 33% of patients. Five patients had experienced venous thrombosis or stroke, but only one of these had hyperhomocysteinemia. Of the 10 IBD patients (15.4%) with hyperhomocysteinemia, only two had vitamin B12 deficiency. The homocysteine levels in the IBD cohort cases and controls were 8.7 and 6.6 micromol/L, respectively (p < 0.05). IBD significantly increased the risk of hyperhomocysteinemia (adjusted odds ratio = 5.9 [95% CI: 1.5-24]). Advanced age, male sex, vitamin B12 deficiency or lower vitamin B12 serum levels, and multivitamin therapy were independently associated with higher homocysteine levels in the multivariate analysis (R2 = 0.55; p = 0.001).

CONCLUSIONS

Hyperhomocysteinemia is significantly more common in patients with IBD compared with healthy controls, and is associated with lower (but not necessarily deficient) vitamin B12 levels.

Expression of inducible nitric oxide synthase and nitrotyrosine in multiple sclerosis lesions

Nitric oxide generated by the inducible form of nitric oxide synthase (iNOS) may contribute to the pathogenesis of multiple sclerosis (MS). In this report, we studied postmortem tissues of MS patients for the expression of iNOS by in situ hybridization and immunocytochemistry. Immunocytochemistry for nitrotyrosine, a putative footprint for peroxynitrite formation was also performed. In acute MS lesions, intense reactivity for iNOS mRNA and protein was detected in reactive astrocytes throughout the lesion and in adjacent normal appearing white matter. Staining of macrophages, inflammatory cell infiltrates, and endothelial cells was variable from case to case, but generally detected only in acute lesions. In chronic MS lesions reactive astrocytes at the lesion edge were positive for iNOS whereas the lesion center was nonreactive. Normal appearing white matter demonstrated little reactivity, as did tissues from noninflamed control brains. Staining for nitrotyrosine was also detected in acute but not chronic MS lesions, and displayed a diffuse parenchymal, membranous, and perivascular pattern of immunoreactivity. These results support the conclusion that iNOS is induced in multiple cell types in MS lesions and that astrocyte-derived nitric oxide could be important in orchestrating inflammatory responses in MS, particularly at the blood-brain barrier.

Increased urinary nitrite, a marker of nitric oxide, in active inflammatory bowel disease

BACKGROUND

Nitric oxide (NO) production is increased in inflammatory bowel disease (IBD), and measurement of NO metabolites may be useful for monitoring disease activity.

AIMS AND OBJECTIVES

To characterise urinary nitrite levels, a stable metabolite of NO, in IBD and to evaluate its potential as a marker of disease activity.

METHODS

Twelve-hour urinary nitrites were measured by the microplate assay method in 46 patients with IBD (active; n = 32). Urinary samples from 16 healthy individuals served as controls.

RESULTS

Increased levels of urinary nitrites were found in patients with active IBD compared with those with inactive IBD. Twenty-eight out of 32 patients (87.5%) with active IBD had detectable levels of nitrite in their urine as compared with 2/14 (14.3%) patients with inactive IBD. None of the 16 healthy controls had detectable urinary nitrite. Twelve-hour urinary nitrite in active compared with inactive IBD: 5 0.7 versus 0.1+/-0.04 micromol (P < 0.05). There was good correlation between urinary nitrite and some markers of disease activity in IBD such as C-reactive protein and microalbuminuria but not with erythrocyte sedimentation rate.

CONCLUSIONS

Increased levels of nitrite were detected in urine of patients with active IBD, consistent with increased NO synthesis. This simple assay may be exploited as a potential marker of disease activity in IBD.

Effect of ecabet sodium enema on mildly to moderately active ulcerative proctosigmoiditis: an open-label study

OBJECTIVES

Ecabet sodium (ES), a nonabsorbable antigastric ulcer agent, has been shown to adhere to the region of an ulcer. It topically enhances gastric mucosal defensive factors such as the endogenous prostaglandins, capsaicin-sensitive sensory nerves, nitric oxide, and mucin. All of these mucosal defensive factors play an important role in maintaining the mucosal integrity of the colon and rectum. Therefore, we investigated the effect of ES in patients with mildly to moderately active ulcerative proctosigmoiditis.

METHODS

In an open-label study, seven patients with mildly to moderately active ulcerative colitis (UC) who had an inflamed mucosa in the rectum and/or sigmoid and were resistant to 4-wk topical and systemic standard treatment were treated with an ES enema b.i.d. for 14 days. The enema consisted of ES (1 g) and tepid water (20 or 50 ml). These patients were assessed by the Clinical Activity Index, colonoscopically, and histologically before and after the ES therapy. The ES therapy was started after obtaining informed consent from the patients.

RESULTS

Six of the seven patients responded to therapy and achieved clinical, endoscopic, and histological remissions. One patient was withdrawn because of increased stool frequency. All six patients who completed the study showed a significant change in the mean Clinical Activity Index score from 5.3+/-1.4 (mean +/- SD) to 0.5+/-0.8 (p < 0.05), in the colonoscopic score from 3.0+/-0.9 to 0.8+/-0.4 (p < 0.05), and in the histological score from 2.7+/-0.5 to 0.5+/-0.6 (p < 0.05), and achieved remission at the end of the study. There were no side effects attributable to the ES therapy. Five of the six patients are still in clinical remission after a median follow-up period of 5 months.

CONCLUSIONS

The ES enemas proved to be a safe and potentially useful adjuvant therapy currently available for treating patients with mildly to moderately active ulcerative proctosigmoiditis. A controlled study is necessary to confirm our results.

Regulation of intestinal regeneration: new insights

Intestinal regeneration is the process by which intestinal injury penetrating deep to the lamina propria heals. The regenerative process involves epithelial cell migration and proliferation, changes in cellular function, adaptation of subepithelial tissues, and contraction of the injured area. This requires interaction of multiple cell types. While many observations have been made about the process of regeneration, its regulation is not well understood. Previous studies, performed primarily in a serosal patch model, have identified many potential regulatory factors. These include location and size of the injury, other associated injury, e.g., resection, and a variety of agents that influence one or more of the primary processes involved. Epidermal growth factor (EGF), in particular, appears to play a role in many aspects of regeneration. Recent advances in the understanding of intestinal growth regulation have provided new insights into the regulation of intestinal regeneration. Developmental studies in genetically manipulated mice suggest a role for gene products not previously implicated in regeneration. The importance of apoptosis in growth regulation has recently been emphasized. Mesenchymal-epithelial interactions have gained greater appreciation. Finally, it has become clear that immune cells and cytokines are important factors in this process. Transforming growth factor-beta (TGFbeta) has been implicated as another important regulator of several of the processes involved in intestinal regulation. Improved understanding of the regulation of intestinal regeneration will lead to new therapeutic approaches to stimulate intestinal healing in the clinical setting.

Cytokine-induced impairment of short-chain fatty acid oxidation and viability in human colonic epithelial cells

Pro-inflammatory cytokines may directly influence the viability and metabolic function of colonic epithelial cells (CEC) as an early event in the development of inflammatory bowel disease. We report here that TNF-alpha+IFN-gamma induced a synergistic, concentration-dependent decline in butyrate oxidation, an essential energy supply, in HT-29 and DLD-1 cells. TNF-alpha+IFN-gamma induced a parallel profound decline in cell viability in HT-29 cells, but not in DLD-1 cells, where impairment of butyrate oxidation seemed to precede later occurrence of cell damage. TNF-alpha+INF-gamma induced CEC damage was independent on NO formation and involved the IFN-gamma signalling pathway as well as induction of apoptosis. If cytokines have similar effects in vivo, these may lead to energy deficiency and thus contribute to CEC damage and disturbance of the epithelial integrity.

Spontaneously developing chronic colitis in IL-10/iNOS double-deficient mice

Mice deficient in both inducible nitric oxide synthase (iNOS) and interleukin (IL)-10 (iNOS(-/-)/IL-10(-/-)) were created to examine the role of iNOS in spontaneously developing intestinal inflammation. IL-10(-/-)/iNOS(-/-) mice were compared with IL-10(-/-) (iNOS(+/+)) littermates over 6 mo. RT-PCR, Western blot analysis, and immunohistochemistry were performed to measure iNOS message and protein levels. Plasma nitrate/nitrite (NO(x)) levels were assessed by HPLC. Damage scores (macroscopic and microscopic) and granulocyte infiltration were assessed. At 3-4 wk, IL-10(-/-) and IL-10(-/-)/iNOS(-/-) mice had no signs of colonic inflammation or granulocyte infiltration. Plasma NO(x) levels were not different from controls. By 3-4 mo, IL-10(-/-) mice had increased damage scores and granulocyte infiltration concurrent with increased mRNA and protein synthesis (restricted to the epithelium) for iNOS in intestinal tissues but not other tissues. Plasma NO(x) levels increased fivefold. Interestingly, in the absence of iNOS induction or increased plasma NO(x), iNOS(-/-)/IL-10(-/-) mice had damage and granulocyte infiltration equivalent to those observed in IL-10(-/-) littermates. These data suggest that iNOS does not impact on the development or severity of spontaneous chronic inflammation in IL-10-deficient mice.

Medical therapy for ulcerative colitis

Last year was not a banner year for developments in medical therapy for ulcerative colitis. In contrast to the expansion of therapies for Crohn disease, treatment for ulcerative colitis was evolutionary, at best, leading many patients to seek alternative medical approaches. Nevertheless, there have been advances in the application of aminosalicylates and immune modifiers for ulcerative colitis. Additional, nonconventional approaches include nicotine, probiotics, dietary therapies, and heparins. Several novel approaches have arisen from animal models, including additional means of inhibiting nuclear factor-kappaB and targeting of tumor necrosis factor-alpha.

Importance of nitric oxide in the regulation of burn oedema, proteinuria and urine output

Burn injuries trigger a pronounced inflammatory response in the burned skin, resulting in oedema formation and impaired circulation. This response involves activation of the nitric oxide (NO) synthetic pathway, which could play a key role in the complex hemodynamic and hemostatic changes occurring as a result of a burn trauma. The results presented in full-thickness skin burns of rats show that the NO-precursor, L-arginine (n = 10), inhibit burn-induced plasma extravasation as compared to saline-treated burned controls (n = 10) (p<0.001) to a level not significantly different from nonburned animals. Administration of the NO-synthase inhibitor. NG-nitro-L-arginine (L-NNA) (n = 10), did not significantly influence burn extravasation compared to burned controls. Accumulated urine volume 90 min post-burn increased ten-fold in burned animals treated with L-arginine compared to saline-treated burned controls (p<0.001) and nonburned animals (p<0.001), while L-NNA had no significant effect on diuresis. A significantly increased proteinuria occurred in L-arginine treated burned animals as compared to burned controls and nonburned controls (p<0.001), whereas L-NNA did not significantly influence the leakage of protein in the urine. Activation of NO synthesis significantly suppresses burn edema and strongly increases diuresis along with increased proteinuria.