Optimizing post-acute coronary syndrome (ACS) dyslipidemia management: Insights from the North American Acute Coronary Syndrome ACS Reflective III

BACKGROUND

Despite contemporary practice guidelines, a substantial number of post-acute coronary syndrome (ACS) patients fail to achieve guideline-recommended LDL-C thresholds. Our study aims to objectively investigate this evidence-to-practice care gap. Specifically, we aim to identify opportunities where additional lipid-lowering therapies are indicated and explore reasons for the non-prescription of guideline-recommended therapies.

METHODS

ACS patients with LDL-C ≥1.81 mmol/L (70 mg/dL) despite maximally tolerated statin ± ezetimibe therapy (including those intolerant of ≥2 statins) were enrolled 1-12 months post-event from 27 Canadian and United States (U.S.) sites from September 2018 to October 2020 and followed up for three visits during the 12 months post-event. We determined the proportion of patients who did not achieve Canadian/U.S. guideline-recommended LDL-C thresholds, the number of patients who would have been eligible for additional lipid-lowering therapies, and reasons behind lack of escalation in lipid-lowering therapies when indicated. Individual patient and aggregate practice feedback, including guideline-recommended intensification suggestions were provided to each physician.

RESULTS

Of the 248 patients enrolled in the pilot study (median age 64 [57, 73] years, 31.5% ¬¬¬¬-female and STEMI 27.4%), 75.4% were on high-intensity statins on the first visit. 18.5% of those who attended all 3 visits had an LDL-C measured only at the first visit which was above the threshold. After one year of follow-up, 51.9% of patients achieved LDL-C thresholds at either visit 2 or 3. In the context of feedback reminding physicians about guideline-directed LDL-C-modifying therapy in their individual participating patients, we observed an increase in the use of ezetimibe and PCSK9 inhibitor therapy at 3-12 months. This was associated with a significant lowering of the mean LDL-C (from 2.93 mmol/L [baseline] to 2.09 mmol/L [3-6 months] to 1.87 mmol/L [6-12 months]) and a significantly greater proportion of patients (from 0% [baseline] to 38.6% [3-6 months] to 53.4% [6-12 months]) achieving guideline-recommended LDL-C thresholds. The most prevalent reasons behind the non-intensification of LDL-C lowering therapy with ezetimibe and/or PCSK9i were LDL-C levels being close to target, the pre-existing use of other lipid-lowering therapies, patient refusal, and cost.

CONCLUSION

Although most patients post-ACS are on high-intensity statin therapy, almost 50% failed to achieve guideline-recommended LDL-C thresholds by 1-year follow-up. Furthermore, additional lipid-lowering therapies in this high-risk group were underprescribed, and this may be linked to several factors including potential gaps in physician knowledge, treatment inertia, patient refusal, and cost.

Provision of a DAPT Score to Cardiologists and Extension of Dual Antiplatelet Therapy Beyond 1 Year After ACS: Randomized Substudy of the Prospective Canadian ACS Reflective II Study

Background

Extension of dual antiplatelet therapy (DAPT) beyond 1 year after acute coronary syndrome is associated with a reduction in ischemic events but also increased bleeding. The DAPT score identifies individuals likely to derive overall benefit or harm from DAPT extension. We sought to evaluate the impact of providing the DAPT score to treating physicians on the decision to extend DAPT beyond 1 year after non–ST-segment elevation myocardial infarction.

Methods

Moderate to high-risk non–ST-segment elevation myocardial infarction patients were enrolled from July 2016 to May 2018 in 13 Canadian hospitals by 52 cardiologists. Participating cardiologists were randomly assigned 1:1 to receive their individual patients’ DAPT scores before the 1-year follow-up visit vs not receiving their patients’ DAPT scores. Rates of DAPT extension were compared among the randomized groups.

Results

At 1 year, 370 of the 585 (63.2%) patients discharged on DAPT were receiving DAPT. Among patients on DAPT at 1 year, the median (25th, 75th percentile) DAPT score was 2 (1,3). DAPT was extended beyond 1 year in 36.2% randomly assigned to provision of DAPT score vs 35.7% in the control group (P = 0.93). In the subgroup of patients with DAPT score ≥ 2, DAPT extension was 49.5% in the DAPT score provision arm vs 40.4% in the control arm (P = 0.22); among patients with DAPT score < 2, DAPT termination was 78.6% in the DAPT score provision arm vs 70.6% in the control arm (P = 0.26) (P value for interaction = 0.1).

Conclusions

In this exploratory randomized trial, provision of the DAPT score to treating physicians had no impact on the duration of DAPT treatment beyond 1 year.

Contemporary use of guideline-based higher potency P2Y12 receptor inhibitor therapy in patients with moderate-to-high risk non-ST-segment elevation myocardial infarction: Results from the Canadian ACS reflective II cross-sectional study

Background

After myocardial infarction, guidelines recommend higher‐potency P2Y12 receptor inhibitors, namely ticagrelor and prasugrel, over clopidogrel.

Hypothesis

We aimed to determine the contemporary use of higher‐potency antiplatelet therapy in Canadian patients with non‐ST‐elevation myocardial infarction (NSTEMI).

Methods

A total of 684 moderate‐to‐high risk NSTEMI patients were enrolled in the prospective Canadian ACS Reflective II registry at 12 Canadian hospitals and three clinics in five provinces between July 2016 and May 2018. Multivariable logistic regression modeling was performed to assess factors independently associated with higher‐potency P2Y12 receptor inhibitor use at discharge.

Results

At hospital discharge, 78.3% of patients were treated with a P2Y12 receptor inhibitor. Among patients discharged on a P2Y12 receptor inhibitor, use of higher‐potency P2Y12 receptor inhibitor was 61.4%. After adjustment, treatment in‐hospital with PCI (OR 4.48, 95%CI 3.34–6.03, p < .0001) was most strongly associated with higher use of higher‐potency P2Y12 receptor inhibitor, while oral anticoagulant use at discharge (OR 0.03, 95%CI 0.01–0.12, p < .0001), and atrial fibrillation (OR 0.40, 95%CI 0.17–0.98, p = .046) were most strongly associated with lower use of higher‐potency P2Y12 receptor inhibitor. Use of higher‐potency P2Y12 receptor inhibitor varied across provinces (range, 21.6%–78.9%).

Discussion

In contemporary Canadian practice, approximately 60% of moderate‐to‐high risk NSTEMI patients discharged on a P2Y12 receptor inhibitor are treated with a higher‐potency P2Y12 receptor inhibitor. In addition to factors that increase risk of bleeding, interprovincial differences in practice patterns were associated with use of higher‐potency P2Y12 receptor inhibitor at discharge. Opportunities remain for further optimization of evidence‐based, guideline‐recommended antiplatelet therapy use.

Acute and chronic effects of glyceryl trinitrate therapy on insulin and glucose regulation in humans

This study examined the effect of acute and sustained transdermal glyceryl trinitrate (GTN) therapy on insulin and glucose regulation. Totally, 12 males (18-30 years) underwent a glucose tolerance test at baseline (visit 1), 90 minutes after acute transdermal GTN 0.6 mg/h (visit 2), following 7 days of continuous GTN (visit 3), and 2 to 3 days after stopping GTN (visit 4). At each visit, plasma glucose and insulin concentrations were measured before and 30, 60, 90, and 120 minutes after a 75-g oral glucose load. Indices of glucose metabolism that were examined included the insulin sensitivity index, the homeostasis model assessment of insulin resistance (HOMA-IR), and the insulinogenic index. The acute administration of GTN had no effect on glucose and insulin responses (visit 2). However, after 7 days of GTN exposure (visit 3) there was an increase in the mean glucose concentration measured after the oral glucose load. On visit 1, the mean glucose concentration (± standard deviation) following the 75 g oral glucose challenge was 5.7 ± 0.5 µmol/L. On visit 3, after 7 days of transdermal GTN therapy, the mean glucose concentration after the oral glucose was significantly higher; 6.2 ± 0.5 µmol/L (P < .015; 95% confidence intervals 0.25-0.77). There was also an increase in the HOMA-IR index; on visit 1, the median HOMA-IR (interquartile range) was 5.2 (3.9) versus 6.9 (6.8) on visit 3 (P < .015). Other indices of glucose metabolism did not change. These observations document that GTN therapy modifies glucose metabolism causing evidence of increased insulin resistance during sustained therapy in normal humans.

Quantification of mitral valve anatomy by three-dimensional transesophageal echocardiography in mitral valve prolapse predicts surgical anatomy and the complexity of mitral valve repair

BACKGROUND

Three-dimensional (3D) transesophageal echocardiography (TEE) is more accurate than two-dimensional (2D) TEE in the qualitative assessment of mitral valve (MV) prolapse (MVP). However, the accuracy of 3D TEE in quantifying MV anatomy is less well studied, and its clinical relevance for MV repair is unknown.

METHODS

The number of prolapsed segments, leaflet heights, and annular dimensions were assessed using 2D and 3D TEE and compared with surgical measurements in 50 patients (mean age, 61 ± 11 years) who underwent MV repair for mainly advanced MVP.

RESULTS

Three-dimensional TEE was more accurate (92%-100%) than 2D TEE (80%-96%) in identifying prolapsed segments. Three-dimensional TEE and intraoperative measurements of leaflet height did not differ significantly, while 2D TEE significantly overestimated the height of the posterior segment P1 and the anterior segment A2. Three-dimensional TEE quantitative MV measurements were related to surgical technique: patients with more complex MVP (one vs two to four vs five or more prolapsed segments) showed progressive enlargement of annular anteroposterior (31 ± 5 vs 34 ± 4 vs 37 ± 6 mm, respectively, P = .02) and commissural diameters (40 ± 6 vs 44 ± 5 vs 50 ± 10 mm, respectively, P = .04) and needed increasingly complex MV repair with larger annuloplasty bands (60 ± 13 vs 67 ± 9 vs 72 ± 10 mm, P = .02) and more neochordae (7 ± 3 vs 12 ± 5 vs 26 ± 6, P < .01).

CONCLUSIONS

Measurements of MV anatomy on 3D TEE are accurate compared with surgical measurements. Quantitative MV characteristics, as assessed by 3D TEE, determined the complexity of MV repair.

Daily low-dose folic acid supplementation does not prevent nitroglycerin-induced nitric oxide synthase dysfunction and tolerance: a human in vivo study

INTRODUCTION

Continuous treatment with nitroglycerin (GTN) causes tolerance and endothelial dysfunction, both of which may involve endothelial nitric oxide synthase (eNOS) dysfunction. eNOS dysfunction may be linked to depletion of tetrahydrobiopterin, and folic acid may be involved in the regeneration of this cofactor. It has been demonstrated that 10 mg⁄day folic acid supplementation prevents the development of GTN tolerance and GTN-induced endothelial dysfunction. However, the efficacy of daily lower-dose folic acid supplementation for preventing these phenomena has not been investigated.

OBJECTIVE

To determine the effect of 1 mg⁄day folic acid supplementation on responses to sustained GTN therapy.

METHODS AND RESULTS

On visit 1, 20 healthy male volunteers were randomly assigned to receive either oral folic acid (1 mg⁄day) or placebo for one week in a double- blind study. All subjects also received continuous transdermal GTN (0.6 mg⁄h). On visit 2, forearm blood flow was measured using venous occlusion strain-gauge plethysmography in response to incremental intra-arterial infusions of acetylcholine, N-monomethyl-L-arginine and GTN. Subjects in both groups displayed significantly decreased responses to acetylcholine and N-monomethyl-L-arginine infusions compared with a control group that received no treatment. Responses to GTN were also significantly diminished in both groups (P<0.05 for all).

DISCUSSION

The present data demonstrate that daily supplementation with 1 mg folic acid does not prevent the development of GTN-induced eNOS dysfunction or tolerance.

Evaluation of left ventricular ejection fraction in non-ST-segment elevation acute coronary syndromes and its relationship to treatment

BACKGROUND

In-hospital assessment of left ventricular ejection fraction (LVEF) in non-ST-segment elevation acute coronary syndrome (NSTE-ACS) is emphasized in current practice guidelines. There are limited data regarding the evaluation of LVEF and clinical characteristics and in-hospital management in the "real world."

METHODS

Registries including the Canadian Acute Coronary Syndrome (ACS) I and II, Global Registry of Acute Coronary Events (main GRACE/expanded GRACE(2)), and Canadian Registry of Acute Coronary Events (CANRACE) enrolled 13,703 NSTE-ACS patients across Canada between 1999 and 2008. Patients were stratified by in-hospital LVEF measurement, and LVEF was categorized as normal, mildly, or moderately to severely impaired. We compared clinical characteristics, cardiac procedures, and clinical outcomes across these groups. Multivariable logistic regression identified factors independently associated with the assessment of LVEF.

RESULTS

Overall, 8,116 patients (59.2%) had LVEF measurement, and of the 7,667 patients with available LVEF data, 4,470 (58.3%) had normal, 1,916 (25%) mildly impaired, and 1,281 (16.7%) moderately to severely impaired LVEF. Patients with LVEF assessment more frequently (all P < .001) underwent cardiac catheterization, percutaneous coronary intervention or coronary bypass surgery, and had higher (both P < .001) rates of myocardial (re) infarction and heart failure. In-hospital reinfarction, higher Killip class, abnormal biomarker, hospital stay >10 days, and on-site cardiac catheterization facility were independently associated with LVEF assessment. Despite increasing LVEF assessment over time (P for trend < .001), 31.2% of patients in the most recent registry (2008) had no in-hospital LVEF assessment.

CONCLUSIONS

In-hospital LVEF assessment is not performed in many NSTE-ACS patients. The LVEF assessment, associated with increased use of evidence-based therapies and invasive cardiac procedures, was obtained more frequently in patients with myocardial (re) infarction, heart failure on presentation, and prolonged hospital stay.

Temporal trends in the use of invasive cardiac procedures for non-ST segment elevation acute coronary syndromes according to initial risk stratification

BACKGROUND

Current guidelines support an early invasive strategy in the management of high-risk non-ST elevation acute coronary syndromes (NSTE-ACS). Although studies in the 1990s suggested that highrisk patients received less aggressive treatment, there are limited data on the contemporary management patterns of NSTE-ACS in Canada.

OBJECTIVE

To examine the in-hospital use of coronary angiography and revascularization in relation to risk among less selected patients with NSTE-ACS.

METHODS

Data from the prospective, multicentre Global Registry of Acute Coronary Events (main GRACE and expanded GRACE2) were used. Between June 1999 and September 2007, 7131 patients from across Canada with a final diagnosis of NSTE-ACS were included the study. The study population was stratified into low-, intermediate- and high-risk groups, based on their calculated GRACE risk score (a validated predictor of in-hospital mortality) and according to time of enrollment.

RESULTS

While rates of in-hospital death and reinfarction were significantly (P<0.001) greater in higher-risk patients, the in-hospital use of cardiac catheterization in low- (64.7%), intermediate- (60.3%) and highrisk (42.3%) patients showed an inverse relationship (P<0.001). This trend persisted despite the increase in the overall rates of cardiac catheterization over time (47.9% in 1999 to 2003 versus 51.6% in 2004 to 2005 versus 63.8% in 2006 to 2007; P<0.001). After adjusting for confounders, intermediate-risk (adjusted OR 0.80 [95% CI 0.70 to 0.92], P=0.002) and high-risk (adjusted OR 0.38 [95% CI 0.29 to 0.48], P<0.001) patients remained less likely to undergo in-hospital cardiac catheterization.

CONCLUSION

Despite the temporal increase in the use of invasive cardiac procedures, they remain paradoxically targeted toward low-risk patients with NSTE-ACS in contemporary practice. This treatment-risk paradox needs to be further addressed to maximize the benefits of invasive therapies in Canada.

Resident CD8+ T cells suppress CD4+ T cell–dependent late allergic airway responses

BACKGROUND

The role of CD8+ T cells in the immune response to airway challenge with an allergen is poorly understood.

OBJECTIVE

The aim of this study was to test the hypothesis that resident naive CD8+ T cells modulate the magnitude of CD4+ T cell-dependent allergic airway responses.

METHODS

Cervical lymph node CD4+ T cells (2 x 10(6)) were harvested from ovalbumin (OVA)- or sham-sensitized rats and injected intraperitoneally into naive Brown Norway recipients. The recipients were treated with a CD8alpha mAb (OX-8) to deplete the resident CD8+ T cells (n = 12) or mouse ascites (n = 12). Two days after adoptive transfer, the recipient animals were OVA challenged, lung resistance was measured for 8 hours, and bronchoalveolar lavage (BAL) was performed.

RESULTS

After OVA challenge, primed CD4-transferred CD8-depleted rats had larger early airway responses and late airway responses compared with primed CD4-transferred CD8-nondepleted rats (early airway responses: 158.6% +/- 19.2% vs 115.7% +/- 5.9%, P < .05; late airway responses: 8.5% +/- 1.7% vs 4.4% +/- 0.9%, P < .05). BAL eosinophilia was also greater (4.67% +/- 0.45% vs 2.34 +/- 0.26%, P < .01). The cells in BAL fluid expressing IL-4 mRNA were not significantly changed by CD8 depletion, but IL-5 mRNA+ cells were higher in number, and IFN-gamma mRNA+ cells were fewer in the CD8-depleted group.

CONCLUSIONS

Resident CD8+ T cells downregulate the late allergic response and airway inflammation evoked by CD4+ T-cell transfers in Brown Norway rats. This downregulation does not require antigen priming.

IL-4 differentially regulates eotaxin and MCP-4 in lung epithelium and circulating mononuclear cells

To investigate the mechanisms of eosinophil recruitment in allergic airway inflammation, we examined the effects of interleukin (IL)-4, a Th2-type cytokine, on eotaxin and monocyte chemoattractant protein-4 (MCP-4) expression in human peripheral blood mononuclear cells (PBMCs; n = 10), in human lower airway mononuclear cells (n = 5), in the human lung epithelial cell lines A549 and BEAS-2B, and in human cultured airway epithelial cells. IL-4 inhibited eotaxin and MCP-4 mRNA expression induced by IL-1 beta and tumor necrosis factor-alpha in PBMCs but did not significantly inhibit expression in epithelial cells. Eotaxin and MCP-4 mRNA expression was not significantly induced by proinflammatory cytokines in lower airway mononuclear cells. IL-1 beta-induced eotaxin and MCP-4 protein production was also inhibited by IL-4 in PBMCs, whereas IL-4 enhanced eotaxin protein production in A549 cells. In contrast, dexamethasone inhibited eotaxin and MCP-4 expression in both PBMCs and epithelial cells. The divergent effects of IL-4 on eotaxin and MCP-4 expression between PBMCs and epithelial cells may create chemokine concentration gradients between the subepithelial layer and the capillary spaces that may promote the recruitment of eosinophils to the airway in Th2-type responses.

IL-1beta induces eotaxin gene transcription in A549 airway epithelial cells through NF-kappaB

Eotaxin is an asthma-related C-C chemokine that is produced in response to interleukin-1beta (IL-1beta). We detected an increase in newly transcribed eotaxin mRNA in IL-1beta-stimulated airway epithelial cells. Transient transfection assays using promoter-reporter constructs identified a region as essential for IL-1beta-induced increases in eotaxin transcription. Using site-directed mutagenesis, we found that a nuclear factor-kappaB (NF-kappaB) site located 46 bp upstream from the transcriptional start site was both necessary and sufficient for IL-1beta induction of reporter construct activity. Electrophoretic mobility shift assay demonstrated that IL-1beta-stimulated airway epithelial cells produced p50 and p65 protein that bound this site in a sequence-specific manner. The functional importance of the NF-kappaB site was demonstrated by coexpression experiments in which increasing doses of p65 expression vector were directly associated with reporter activity exclusively in constructs with an intact NF-kappaB site (r(2) = 0.97, P = 0.002). Moreover, IL-1beta-induced increases in eotaxin mRNA expression are inhibited by inhibitors of NF-kappaB. Our findings implicate NF-kappaB and its binding sequence in IL-1beta-induced transcriptional activation of the eotaxin gene.

Monocyte chemoattractant protein (MCP)-4 expression in the airways of patients with asthma. Induction in epithelial cells and mononuclear cells by proinflammatory cytokines

Chemokines are chemotactic cytokines that play an important role in recruiting leukocytes in allergic inflammation. Monocyte chemoacctractant protein (MCP)-4 is a CC chemokine with potent chemotactic activities for eosinophils, monocytes, T lymphocytes, and basophils and therefore represents a good candidate to participate in allergic reactions. To determine if MCP-4 plays a role in asthma, we have investigated the expression of MCP-4 messenger RNA (mRNA) and protein in the airways of patients with asthma and normal control subjects by in situ hybridization and immunohistochemistry. We found that MCP-4 mRNA and protein was significantly upregulated in the epithelium and submucosa of bronchial biopsies and in the bronchoalveolar lavage (BAL) cells of patients with asthma compared with normal control subjects (p < 0. 01). In addition, MCP-4 protein was significantly elevated in the BAL fluid of patients with atopic asthma when compared with normal control subjects (p < 0.01) and there was a significant correlation between MCP-4, eotaxin, and eosinophils. In support of our in situ findings demonstrating MCP-4 expression in epithelial cells and mononuclear cells in vivo, we have found that MCP-4 expression can be induced in these cells in vitro by tumor necrosis factor-alpha (TNF-alpha) and interleukin-1beta (IL-1beta). Interferon-gamma (IFN-gamma) acted synergistically with TNF-alpha and IL-1beta in the induction of mRNA MCP-4 mRNA expression in A549 cells, whereas the glucocorticoid dexamethasone diminished the cytokine-induced expression of MCP-4. Our findings demonstrate that MCP-4 is upregulated in the airways of patients with asthma and suggest that MCP-4 plays a role in the recruitment of eosinophils into the airways of patients with asthma.

Superantigen immune stimulation evokes epithelial monocyte chemoattractant protein 1 and RANTES production

Bacterial superantigens (SAgs) have been implicated in inflammatory disease, and SAg-treated mice have increased jejunal T cells. Here we show that T84 cells (a human epithelial cell line) display increased MCP-1 and RANTES mRNA expression and protein production in response to conditioned medium from Staphylococcus aureus enterotoxin B (SEB; a model SAg)-activated immune cells. Also, MCP-1 and RANTES mRNAs were increased in jejunal enterocytes isolated from SEB-treated mice. We suggest that T-cell recruitment to the gut following SAg immune activation could be partially due to epithelium-derived chemokines.

Nitric Oxide Participates in the Recovery of Normal Jejunal Epithelial Ion Transport Following Exposure to the Superantigen, Staphylococcus aureus Enterotoxin B

Bacterial superantigens (SAgs) are potent T cell activators. Mice treated 4 h previously with the SAg, Staphylococcus aureus enterotoxin B (SEB), display reduced ion transport (assessed by short circuit current) responses to prosecretory stimuli, which normalize 24 h posttreatment. Here, mice were treated with SEB alone or in combination with an inhibitor of the inducible form of NO synthase (iNOS), l-NIL. Subsequently, jejunal iNOS expression was detected by immunohistochemistry, ion transport was evaluated in Ussing chambers, and serum levels of TNF-α and IFN-γ were measured by ELISA. SEB-treated mice had increased epithelial iNOS immunoreactivity, and numerous iNOS-positive CD3+ T cells occurred in their mucosa and submucosa. Concomitant treatment with l-NIL did not affect the reduced short circuit current responsiveness to electrical nerve stimulation or the prosecretory agents, carbachol and forskolin, that occurred 4 h post-SEB (5 μg) treatment. However, Isc responses in l-NIL- plus SEB-treated mice were still significantly reduced 24 h posttreatment, indicating a role for NO in the restoration of normal ion transport following exposure to SAgs. The prolongation of epithelial ion transport abnormalities correlated with elevated serum levels of TNF-α and IFN-γ in mice treated 24 h previously with l-NIL plus SEB compared with those in controls and SEB-only-treated mice. Additionally, mice treated with l-NIL plus SEB and TNF-α- or IFN-γ-neutralizing Abs displayed normal jejunal ion transport characteristics 24 h posttreatment. We conclude that NO mobilization is important in the homeostatic recovery response following immune stimulation by SAgs and that the beneficial effect of NO in this model system is probably via regulation of TNF-α and IFN-γ production.

Nitric oxide participates in the recovery of normal jejunal epithelial ion transport following exposure to the superantigen, Staphylococcus aureus enterotoxin B

Bacterial superantigens (SAgs) are potent T cell activators. Mice treated 4 h previously with the SAg, Staphylococcus aureus enterotoxin B (SEB), display reduced ion transport (assessed by short circuit current) responses to prosecretory stimuli, which normalize 24 h posttreatment. Here, mice were treated with SEB alone or in combination with an inhibitor of the inducible form of NO synthase (iNOS), l -NIL. Subsequently, jejunal iNOS expression was detected by immunohistochemistry, ion transport was evaluated in Ussing chambers, and serum levels of TNF-alpha and IFN-gamma were measured by ELISA. SEB-treated mice had increased epithelial iNOS immunoreactivity, and numerous iNOS-positive CD3+ T cells occurred in their mucosa and submucosa. Concomitant treatment with l -NIL did not affect the reduced short circuit current responsiveness to electrical nerve stimulation or the prosecretory agents, carbachol and forskolin, that occurred 4 h post-SEB (5 microgram) treatment. However, Isc responses in l -NIL- plus SEB-treated mice were still significantly reduced 24 h posttreatment, indicating a role for NO in the restoration of normal ion transport following exposure to SAgs. The prolongation of epithelial ion transport abnormalities correlated with elevated serum levels of TNF-alpha and IFN-gamma in mice treated 24 h previously with l -NIL plus SEB compared with those in controls and SEB-only-treated mice. Additionally, mice treated with l -NIL plus SEB and TNF-alpha- or IFN-gamma-neutralizing Abs displayed normal jejunal ion transport characteristics 24 h posttreatment. We conclude that NO mobilization is important in the homeostatic recovery response following immune stimulation by SAgs and that the beneficial effect of NO in this model system is probably via regulation of TNF-alpha and IFN-gamma production.