Acetylcholine, Fatty Acids, and Lipid Mediators Are Linked to COVID-19 Severity.

Lipid and cholinergic mediators are inflammatory regulators, but their role in the immunopathology of COVID-19 is still unclear. Here, we used human blood and tracheal aspirate (TA) to investigate whether acetylcholine (Ach), fatty acids (FAs), and their derived lipid mediators (LMs) are associated with COVID-19 severity. First, we analyzed the perturbation profile induced by SARS-CoV-2 infection in the transcriptional profile of genes related to the ACh and FA/LM pathways. Blood and TA were used for metabolomic and lipidomic analyses and for quantification of leukocytes, cytokines, and ACh. Differential expression and coexpression gene network data revealed a unique transcriptional profile associated with ACh and FA/LM production, release, and cellular signaling. Transcriptomic data were corroborated by laboratory findings: SARS-CoV-2 infection increased plasma and TA levels of arachidonic acid, 5-hydroxy-6E,8Z,11Z,14Z-eicosatetraenoic acid, 11-hydroxy-5Z,8Z,12E,14Z-eicosatetraenoic acid, and ACh. TA samples also exhibited high levels of PGE2, thromboxane B2, 12-oxo-5Z,8Z,10E,14Z-eicosatetraenoic acid, and 6-trans-leukotriene B4 Bioinformatics and experimental approaches demonstrated robust correlation between transcriptional profile in Ach and FA/LM pathways and parameters of severe COVID-19. As expected, the increased neutrophil-to-lymphocyte ratio, neutrophil counts, and cytokine levels (IL-6, IL-10, IL-1ß, and IL-8) correlated with worse clinical scores. Glucocorticoids protected severe and critical patients and correlated with reduced Ach levels in plasma and TA samples. We demonstrated that pulmonary and systemic hyperinflammation in severe COVID-19 are associated with high levels of Ach and FA/LM. Glucocorticoids favored the survival of patients with severe/critical disease, and this effect was associated with a reduction in ACh levels.

The turning point of COVID-19 severity is associated with a unique circulating neutrophil gene signature.

COVID-19 has a broad spectrum of clinical manifestations associated with the host immune response heterogeneity. Despite the advances in COVID-19 research, it is still crucial to seek a panel of molecular markers that enable accurate stratification of COVID-19 patients. Here, we performed a study that combined analysis of blood transcriptome, demographic data, clinical aspects and laboratory findings from 66 participants classified into different degrees of COVID-19 severity and healthy subjects. We identified a perturbation in blood-leukocyte transcriptional profile associated with COVID-19 aggravation, which was mainly related to processes that disfavoured lymphocyte activation and favoured neutrophil activation. This transcriptional profile stratified patients according to COVID-19 severity. Hence, it enabled identification of a turning point in transcriptional dynamics that distinguished disease outcomes and non-hospitalized from hospitalized moderate patients. Central genes of this unique neutrophil signature were S100A9, ANXA3, CEACAM6, VNN1, OLFM4, IL1R2, TCN1 and CD177. Our study indicates the molecular changes that are linked with the differing clinical aspects presented by humans when suffering from COVID-19, which involve neutrophil activation.

Divergent androgenic modulation of SARS-CoV-2 infection cooperates with dysregulated immune response to dictate worse COVID-19 outcomes in men.

BACKGROUND: Sex-determined differences are rarely addressed in the management of diseases, despite well-known contrasting outcomes between female and male patients. In COVID-19 there is a remarkable disparity, with higher rates of mortality and more severe acute disease in men compared to women, who are mostly affected by long COVID-19. Furthermore, whether androgens play a protective or detrimental role in COVID-19 is still a matter of debate. Hence, the adequate management of the disease, especially regarding men presenting acute disease aggravation, still needs important data to elucidate the interplay between sex hormones and host immune responses that drive the worse evolution in male patients. METHODS: A cohort of 92 controls and 198 non-severe and severe COVID-19 patients, from both sexes, was assessed for clinical outcomes, plasma steroids, gonadotropins, sex hormone binding globulin (SHBG) and immune mediators, before vaccination. These data were correlated with the global gene expression of blood leukocytes. The androgen receptor (AR) signaling pathway was investigated by transcriptomics and tracheal aspirate was obtained from severe patients for SARS-COV-2 quantification in the respiratory tract. The interplay among clinical, endocrine and immunological data deciphered the sex differences in COVID-19. Importantly, statistical analyses, using 95% confidence interval, considered confounding factors such as age and comorbidities, to definitely parse the role of androgens in the disease outcome. RESULTS: There were notable contrasting levels of testosterone and dihydrotestosterone (DHT) throughout the disease course in male but not female patients. Inflammatory mediators presented significant negative correlations with testosterone, which was partially dependent on age and diabetes in men. Male subjects with severe COVID-19 had a significant up regulation of the AR signaling pathway, including modulation of TMPRSS2 and SRD5A1 genes, which are related to the viral infection and DHT production. Indeed, men had a higher viral load in the tracheal aspirate and levels of DHT were associated with increased relative risk of death. In contrast, the testosterone hormone, which was notably reduced in severe disease, was significantly related with susceptibility to COVID-19 worsening in male patients. Secondary hypogonadism was ruled out in the male severe COVID-19 subjects, as FSH, LH, and SHBG levels were not significantly altered. Instead, these subjects tended to have increased gonadotropin levels. Most interestingly, in this study we identified, for the first time, combined sets of clinical and immunoendocrine parameters that together predicted progression from non-severe to severe COVID-19 in men. One of the limitations of our study was the low or undetectable levels of DHT in many patients. Then, the evaluation of enzymes related to biosynthesis and signaling by androgens was mandatory and reiterated our findings. CONCLUSIONS: These original results unraveled the disease immunoendocrine regulation, despite vaccination or comorbidities and pointed to the fundamental divergent role of the androgens testosterone and DHT in the determination of COVID-19 outcomes in men. Therefore, sex-specific management of the dysregulated responses, treatments or public health measures should be considered for the control of COVID-19 pandemic.

The Interplay among Glucocorticoid Therapy, Platelet-Activating Factor and Endocannabinoid Release Influences the Inflammatory Response to COVID-19.

COVID-19 is associated with a dysregulated immune response. Currently, several medicines are licensed for the treatment of this disease. Due to their significant role in inhibiting pro-inflammatory cytokines and lipid mediators, glucocorticoids (GCs) have attracted a great deal of attention. Similarly, the endocannabinoid (eCB) system regulates various physiological processes including the immunological response. Additionally, during inflammatory and thrombotic processes, phospholipids from cell membranes are cleaved to produce platelet-activating factor (PAF), another lipid mediator. Nonetheless, the effect of GCs on this lipid pathway during COVID-19 therapy is still unknown. This is a cross-sectional study involving COVID-19 patients (n = 200) and healthy controls (n = 35). Target tandem mass spectrometry of plasma lipid mediators demonstrated that COVID-19 severity affected eCBs and PAF synthesis. This increased synthesis of eCB was adversely linked with systemic inflammatory markers IL-6 and sTREM-1 levels and neutrophil counts. The use of GCs altered these lipid pathways by reducing PAF and increasing 2-AG production. Corroborating this, transcriptome analysis of GC-treated patients blood leukocytes showed differential modulation of monoacylglycerol lipase and phospholipase A2 gene expression. Altogether, these findings offer a breakthrough in our understanding of COVID-19 pathophysiology, indicating that GCs may promote additional protective pharmacological effects by influencing the eCB and PAF pathways involved in the disease course.

Plasma Sphingomyelin Disturbances: Unveiling Its Dual Role as a Crucial Immunopathological Factor and a Severity Prognostic Biomarker in COVID-19.

SARS-CoV-2 infection triggers distinct patterns of disease development characterized by significant alterations in host regulatory responses. Severe cases exhibit profound lung inflammation and systemic repercussions. Remarkably, critically ill patients display a "lipid storm", influencing the inflammatory process and tissue damage. Sphingolipids (SLs) play pivotal roles in various cellular and tissue processes, including inflammation, metabolic disorders, and cancer. In this study, we employed high-resolution mass spectrometry to investigate SL metabolism in plasma samples obtained from control subjects (n = 55), COVID-19 patients (n = 204), and convalescent individuals (n = 77). These data were correlated with inflammatory parameters associated with the clinical severity of COVID-19. Additionally, we utilized RNAseq analysis to examine the gene expression of enzymes involved in the SL pathway. Our analysis revealed the presence of thirty-eight SL species from seven families in the plasma of study participants. The most profound alterations in the SL species profile were observed in patients with severe disease. Notably, a predominant sphingomyelin (SM d18:1) species emerged as a potential biomarker for COVID-19 severity, showing decreased levels in the plasma of convalescent individuals. Elevated SM levels were positively correlated with age, hospitalization duration, clinical score, and neutrophil count, as well as the production of IL-6 and IL-8. Intriguingly, we identified a putative protective effect against disease severity mediated by SM (d18:1/24:0), while ceramide (Cer) species (d18:1/24:1) and (d18:1/24:0)were associated with increased risk. Moreover, we observed the enhanced expression of key enzymes involved in the SL pathway in blood cells from severe COVID-19 patients, suggesting a primary flow towards Cer generation in tandem with SM synthesis. These findings underscore the potential of SM as a prognostic biomarker for COVID-19 and highlight promising pharmacological targets. By targeting sphingolipid pathways, novel therapeutic strategies may emerge to mitigate the severity of COVID-19 and improve patient outcomes.

Matrix Metalloproteinases on Severe COVID-19 Lung Disease Pathogenesis: Cooperative Actions of MMP-8/MMP-2 Axis on Immune Response through HLA-G Shedding and Oxidative Stress.

Patients with COVID-19 predominantly have a respiratory tract infection and acute lung failure is the most severe complication. While the molecular basis of SARS-CoV-2 immunopathology is still unknown, it is well established that lung infection is associated with hyper-inflammation and tissue damage. Matrix metalloproteinases (MMPs) contribute to tissue destruction in many pathological situations, and the activity of MMPs in the lung leads to the release of bioactive mediators with inflammatory properties. We sought to characterize a scenario in which MMPs could influence the lung pathogenesis of COVID-19. Although we observed high diversity of MMPs in lung tissue from COVID-19 patients by proteomics, we specified the expression and enzyme activity of MMP-2 in tracheal-aspirate fluid (TAF) samples from intubated COVID-19 and non-COVID-19 patients. Moreover, the expression of MMP-8 was positively correlated with MMP-2 levels and possible shedding of the immunosuppression mediator sHLA-G and sTREM-1. Together, overexpression of the MMP-2/MMP-8 axis, in addition to neutrophil infiltration and products, such as reactive oxygen species (ROS), increased lipid peroxidation that could promote intensive destruction of lung tissue in severe COVID-19. Thus, the inhibition of MMPs can be a novel target and promising treatment strategy in severe COVID-19.

Adjunctive Hyperbaric Oxygen Therapy in Refractory Crohn's Disease: An Observational Study.

BACKGROUND AND AIMS: Patients may experience complications of Crohn's disease (CD) even when treated with optimal medical therapy strategies. Previous data have shown the efficacy of hyperbaric oxygen therapy (HBOT) in the management of complicated CD. However, there is no consensus regarding the optimal number of sessions or duration of treatment regimens. The aim of the present study was to investigate the efficacy of HBOT in CD patients who were refractory to conventional medical management. METHODS: This study included patients who underwent HBOT for the treatment of the following complications: perianal fistulizing Crohn's disease (pCD), enterocutaneous fistulas (ECF), or pyoderma gangrenosum (PG). Complete healing was defined as the closure of external orifice and the absence of active draining (in pCD), complete wound healing (in PG), and granulation or complete wound epithelialization with no enteric draining (in ECF). The persistence of draining and the absence of wound granulation were defined as incomplete healing. RESULTS: Forty patients were included. The mean CD duration was 10.6 ± 5.8 years. pCD comprised most of the included patients (25/62.5%), followed by ECF (n = 13/32.5%) and PG (n = 6/15%). In two patients (5%), a combination of ECF and PG was diagnosed, and in one patient (2.5%), all three complications were observed. A total of 32 patients (82.5%) had complete healing. Patients with PG had the highest healing rates (100%), followed by those with ECF (84.6%) and pCD (80%). CONCLUSIONS: Adjunctive HBO was associated with significant healing rates for CD-associated complications such as pCD, ECF, and PG.

Real-world treatment patterns and disease control over one year in patients with inflammatory bowel disease in Brazil.

BACKGROUND: Crohn's disease (CD) and ulcerative colitis (UC) are inflammatory bowel diseases (IBDs) with a remission-relapsing presentation and symptomatic exacerbations that have detrimental impacts on patient quality of life and are associated with a high cost burden, especially in patients with moderate-to-severe disease. The Real-world Data of Moderate-to-Severe Inflammatory Bowel Disease in Brazil (RISE BR) study was a noninterventional study designed to evaluate disease control, treatment patterns, disease burden and health-related quality of life in patients with moderate-to-severe active IBD. We report findings from the prospective follow-up phase of the RISE BR study in patients with active UC or CD. AIM: To describe the 12-mo disease evolution and treatment patterns among patients with active moderate-to-severe IBD in Brazil. METHODS: This was a prospective, noninterventional study of adult patients with active Crohn's disease (CD: Harvey-Bradshaw Index ≥ 8, CD Activity Index ≥ 220), inadequate CD control (i.e., calprotectin > 200 µg/g or colonoscopy previous results), or active ulcerative colitis (UC: Partial Mayo score ≥ 5). Enrollment occurred in 14 centers from October 2016 to February 2017. The proportion of active IBD patients after 9-12 mo of follow-up, Kaplan-Meier estimates of the time to mild or no activity and a summary of treatment initiation, discontinuation and dose changes were examined. RESULTS: The study included 118 CD and 36 UC patients, with mean ± SD ages of 43.3 ± 12.6 and 44.9 ± 16.5 years, respectively. The most frequent drug classes at index were biologics for CD (62.7%) and 5-aminosalicylate derivates for UC patients (91.7%). During follow-up, 65.3% of CD and 86.1% of UC patients initiated a new treatment at least once. Discontinuations/dose changes occurred in 68.1% of CD patients [median 2.0 (IQR: 2-5)] and 94.3% of UC patients [median 4.0 (IQR: 3-7)]. On average, CD and UC patients had 4.4 ± 2.6 and 5.0 ± 3.3 outpatient visits, respectively. The median time to first mild or no activity was 319 (IQR: 239-358) d for CD and 320 (IQR: 288-358) d for UC patients. At 9-12 mo, 22.0% of CD and 20.0% of UC patients had active disease. CONCLUSION: Although a marked proportion of active IBD patients achieved disease control within one year, the considerable time to achieve this outcome represents an unmet medical need of the current standard of care in a Brazilian real-world setting.

sTREM-1 Predicts Disease Severity and Mortality in COVID-19 Patients: Involvement of Peripheral Blood Leukocytes and MMP-8 Activity.

Uncontrolled inflammatory responses play a critical role in coronavirus disease (COVID-19). In this context, because the triggering-receptor expressed on myeloid cells-1 (TREM-1) is considered an intrinsic amplifier of inflammatory signals, this study investigated the role of soluble TREM-1 (sTREM-1) as a biomarker of the severity and mortality of COVID-19. Based on their clinical scores, we enrolled COVID-19 positive patients (n = 237) classified into mild, moderate, severe, and critical groups. Clinical data and patient characteristics were obtained from medical records, and their plasma inflammatory mediator profiles were evaluated with immunoassays. Plasma levels of sTREM-1 were significantly higher among patients with severe disease compared to all other groups. Additionally, levels of sTREM-1 showed a significant positive correlation with other inflammatory parameters, such as IL-6, IL-10, IL-8, and neutrophil counts, and a significant negative correlation was observed with lymphocyte counts. Most interestingly, sTREM-1 was found to be a strong predictive biomarker of the severity of COVID-19 and was related to the worst outcome and death. Systemic levels of sTREM-1 were significantly correlated with the expression of matrix metalloproteinases (MMP)-8, which can release TREM-1 from the surface of peripheral blood cells. Our findings indicated that quantification of sTREM-1 could be used as a predictive tool for disease outcome, thus improving the timing of clinical and pharmacological interventions in patients with COVID-19.

Real-world disease activity and sociodemographic, clinical and treatment characteristics of moderate-to-severe inflammatory bowel disease in Brazil.

BACKGROUND: Understanding the treatment landscape of inflammatory bowel diseases (IBD) is essential for improving disease management and patient outcomes. Brazil is the largest Latin American country, and it presents socioeconomic and health care differences across its geographical regions. This country has the highest increase in IBD incidence and prevalence in Latin America, but information about the clinical and treatment characteristics of IBD is scarce. AIM: To describe the sociodemographic, clinical, and treatment characteristics of IBD outpatients in Brazil overall and in the Southeast, South and Northeast/Midwest regions. METHODS: Multicenter, cross-sectional study with a 3-year retrospective chart review component. Patients with moderate-to-severe Crohn's disease (CD) or ulcerative colitis (UC) were consecutively enrolled between October 2016 and February 2017. Active CD at enrollment was defined as a Harvey Bradshaw Index ≥ 8 or a CD Activity Index ≥ 220 or a calprotectin level > 200 µg/g or an active result based on colonoscopy suggestive of inadequate control during the previous year; active UC was defined as a partial Mayo score ≥ 5. Descriptive statistics were used to analyze all variables. RESULTS: In a total of 407 included patients, CD was more frequent than UC, both overall (264 CD/143 UC patients) and by region (CD:UC ratios of 2.1 in the Southeast, 1.6 in the South and 1.2 in the Northeast/Midwest). The majority of patients were female (54.2% of CD; 56.6% of UC), and the mean ages were 45.9 ± 13.8 years (CD) and 42.9 ± 13.0 years (UC). The median disease duration was 10.0 (range: 0.5-45) years for both IBD types. At enrollment, 44.7% [95% confidence interval (CI): 38.7-50.7] of CD patients and 25.2% (95%CI: 18.1-32.3) of UC patients presented with active disease. More than 95% of IBD patients were receiving treatment at enrollment; CD patients were commonly treated with biologics (71.6%) and immunosuppressors (67.4%), and UC patients were commonly treated with mesalazine [5-Aminosalicylic acid (5-ASA)] derivates (69.9%) and immunosuppressors (44.1%). More than 50% of the CD patients had ileocolonic disease, and 41.7% presented with stricturing disease. One-quarter of CD patients had undergone CD-related surgery in the past 3 years, and this proportion was lower in the Northeast/Midwest region (2.9%). CONCLUSION: In Brazil, there are regional variations in IBD management. CD outweighs UC in both frequency and disease activity. However, one-quarter of UC patients have active disease, and most are receiving 5-ASA treatment.

A Novel Severity Score Index for Febrile Neutropenic Patients with Colorectal Diseases.

INTRODUCTION: Abdominal and anorectal disorders may be the cause of clinical decompensation in neutropenic febrile patients, particularly those with hematologic diseases. Infection is a cause for concern for the colorectal surgeon. Some conditions have few manifestations and can lead to death within a short period of time. This study presents the novel colorectal disorder severity score for febrile neutropenic patients. MATERIALS AND METHODS: This was a case series study analyzing the medical records of 897 patients admitted to the Hematology and Hematopoietic Stem Cell Transplant Unit in a university hospital between the years 2008 and 2013. Seventy-four episodes of febrile neutropenia in 69 patients diagnosed with an abdominal or anorectal infection site were eligible for the study. The new scoring system proposed here is based on the author's clinical experience and an extensive literature review. In addition to the extensive literature review, effect measures were calculated, and a statistical analysis was performed. Based on an evaluation of common biological plausibility criteria, five factors were selected as the main predictors of hospital mortality in febrile neutropenic patients with colorectal disease. RESULTS: The proposed score demonstrated increased mortality as the condition worsened as reflected by an increasing score (Fisher's exact test: 0.001). When considering the logistic model for the probability of death by score level, the AUC value was 0.82 (0.72-0.925), and the Hosmer-Lemeshow statistic value was 2.3, p = 0.806. CONCLUSION: The proposed scoring system allows prediction of the likelihood of death during hospitalization for febrile neutropenic patients with an abdominal and anorectal focus. New studies on the subject are required, and the proposed scoring scale must be validated on a larger and different sample of patients.

Quality of life, work productivity impairment and healthcare resources in inflammatory bowel diseases in Brazil.

BACKGROUND: Inflammatory bowel diseases (IBD) have been associated with a low quality of life (QoL) and a negative impact on work productivity compared to the general population. Information about disease control, patient-reported outcomes (PROs), treatment patterns and use of healthcare resources is relevant to optimizing IBD management. AIM: To describe QoL and work productivity and activity impairment (WPAI), treatment patterns and use of healthcare resources among IBD patients in Brazil. METHODS: A multicenter cross-sectional study included adult outpatients who were previously diagnosed with moderate to severe Crohn's disease (CD) or ulcerative colitis (UC). At enrolment, active CD and UC were defined as having a Harvey Bradshaw Index ≥ 8 or a CD Activity Index ≥ 220 or calprotectin > 200 µg/g or previous colonoscopy results suggestive of inadequate control (per investigator criteria) and a 9-point partial Mayo score ≥ 5, respectively. The PRO assessment included the QoL questionnaires SF-36 and EQ-5D-5L, the Inflammatory Bowel Disease Questionnaire (IBDQ), and the WPAI questionnaire. Information about healthcare resources and treatment during the previous 3 years was collected from medical records. Chi-square, Fisher's exact and Student's t-/Mann-Whitney U tests were used to compare PROs, treatment patterns and the use of healthcare resources by disease activity (α = 0.05). RESULTS: Of the 407 patients in this study (CD/UC: 64.9%/35.1%, mean age 42.9/45.9 years, 54.2%/56.6% female, 38.3%/37.1% employed), 44.7%/25.2% presented moderate-to-severe CD/UC activity, respectively, at baseline. Expressed in median values for CD/UC, respectively, the SF-36 physical component was 46.6/44.7 and the mental component was 45.2/44.2, the EQ-visual analog scale score was 80.0/70.0, and the IBDQ overall score was 164.0/165.0. Moderate to severe activity, female gender, being unemployed, a lower educational level and lower income were associated with lower QoL (P < 0.05). Median work productivity impairment was 20% and 5% for CD and UC patients, respectively, and activity impairment was 30%, the latter being higher among patients with moderate to severe disease activity compared to patients with mild or no disease activity (75.0% vs 10.0%, P < 0.001). For CD/UC patients, respectively, 25.4%/2.8% had at least one surgery, 38.3%/19.6% were hospitalized, and 70.7%/77.6% changed IBD treatment at least once during the last 3 years. The most common treatments at baseline were biologics (75.3%) and immunosuppressants (70.9%) for CD patients and 5-ASA compounds (77.5%) for UC patients. CONCLUSION: Moderate to severe IBD activity, especially among CD patients, is associated with a substantial impact on QoL, work productivity impairment and an increased number of IBD surgeries and hospitalizations in Brazil.

Infliximab Trough Levels and Quality of Life in Patients with Inflammatory Bowel Disease in Maintenance Therapy.

OBJECTIVE: Investigate the association between infliximab trough levels and quality of life in inflammatory bowel disease patients in maintenance therapy. METHODS: We carried out a transversal study with inflammatory bowel disease patients in infliximab maintenance therapy. Infliximab trough levels were determined using a quantitative rapid test. Disease activity indices (partial Mayo Score and Harvey-Bradshaw Index) and endoscopic scores (endoscopic Mayo Score or Simple Endoscopic Score in Crohn's disease) were obtained. Quality of life was assessed using the Inflammatory Bowel Disease Questionnaire (IBDQ). RESULTS: Seventy-one consecutive subjects were included in the study (55 with Crohn's disease and 16 with ulcerative colitis). Drug levels were considered satisfactory (≥3 µg/mL) in 28 patients (39.4%) and unsatisfactory (<3 µg/mL) in 43 (60.6%). Satisfactory trough levels were associated with higher rates of clinical remission and mucosal healing. Higher trough levels were also associated with improved IBDQ scores, particularly regarding bowel symptoms, systemic function, and social function. CONCLUSION: Satisfactory trough levels of infliximab were associated with higher rates of clinical remission, mucosal healing, and improved quality of life in inflammatory bowel disease patients on maintenance therapy.

Hyperbaric oxygen therapy ameliorates TNBS-induced acute distal colitis in rats.

BACKGROUND: This study investigated the therapeutic effects of hyperbaric oxygen in experimental acute distal colitis focusing on its effect on the production of pro-inflammatory cytokines, nitric oxide and hypoxia-inducible factor 1alpha. METHODS: Colitis was induced with a rectal infusion of 150 mg/kg of TNBS under anesthesia with Ketamine (50 mg/kg) and Xylazine (10 mg/kg). Control animals received only rectal saline. After colitis induction, animals were subjected to two sessions of hyperbaric oxygen and were then euthanized. The distal intestine was resected for macroscopic analysis, determination of myeloperoxidase activity, western-blotting analyses of inducible nitric oxide synthase and cyclooxygenase-2 expression and immunohistochemical analysis of hypoxia-inducible factor 1alpha and cyclooxygenase-2. Cytokines levels in the distal intestine were measured using an enzyme-linked immunosorbent assay. RESULTS: Hyperbaric oxygen therapy attenuated the severity of acute distal colitis, with reduced macroscopic damage score. This effect was associated with prevention in the increase of pro-inflammatory cytokine production; myeloperoxidase activity, in the expression of inducible nitric oxide synthase and cyclooxygenase-2. Finally, hyperbaric oxygen inhibited the acute distal colitis-induced up-regulation of hypoxia-inducible factor 1alpha. CONCLUSIONS: The results indicate that hyperbaric oxygen attenuates the severity of acute distal colitis through the down-regulation of pro-inflammatory events.