Histopathological study of carcinoma showing thymus-like differentiation (CASTLE)

INTRODUCTION

Carcinoma showing thymus-like differentiation (CASTLE) is a rare tumour that mainly arises from the thyroid gland, or occasionally, from the head and neck. Although the 10-year survival rate of patients with CASTLE is approximately 80%, local recurrence and distant metastasis are observed in some cases. A recent systematic review for CASTLE indicated that the prognostic factors are treatment-dependent, and postoperative radiotherapy significantly improves patient survival.

CASE REPORT

Herein, we describe and compare three cases of CASTLE, including a case with distant metastasis despite administering postoperative chemotherapy. Thus, the mechanisms underlying metastasis of CASTLE are unclear. This case study helps to elucidate the histopathological risk factors of metastasis in CASTLE.

DISCUSSION

We found that prominent lymphovascular invasion and higher proliferative activities might be risk factors of metastasis in CASTLE. In addition, we have summarised the cytological, morphological, and immunohistochemical features of CASTLE for an accurate diagnosis.

Histamine-2 receptor antagonists (H₂RA) may negatively impact ADL assessment in patients on a convalescent rehabilitation ward

Background/aim: In the convalescent rehabilitation ward, many elderly patients undergo rehabilitation. Histamine-2 receptor antagonists (H₂RA), which is a one of the acid secretion inhibitors, is frequently prescribed for the patients as a peptic ulcer prevention measure. At present, H₂RA are reported as being associated with factors that reduce cognitive function. However, little is known about the relationship H₂RA and rehabilitation outcome. Therefore, this study examined the relationship between H₂RA use and Functional Independence Measure (FIM) gain, which determines rehabilitation outcomes for patients admitted to the convalescent rehabilitation ward. Patients and methods: We retrospectively investigated FIM gain on discharge by both the administration group (H₂RA (+)) (n = 118) and non-administration group (H₂RA (-)) (n = 118). Results: The FIM gain scores of Motor FIM total, Cognition FIM total, and Total FIM were significantly lower in H₂RA (+) than in H₂RA (-) (Motor FIM total: 8.0 [4.0-16.0] [Inter-Quartile Range] vs. 12.0 [5.0-19.2], p =0.0217, Cognition FIM total: 3.0 [1.0-6.0] vs. 5.0 [2.0-7.0], p =0.0120, Total FIM: 11.5 [4.8-20.2] vs. 17.0 [8.0-27.0], p =0.0089). Conclusion: The administration of H₂RA to elderly patients undergoing rehabilitation may prevent cognitive function maintenance or recovery by rehabilitation.

Nintedanib in patients with progressive fibrosing interstitial lung diseases-subgroup analyses by interstitial lung disease diagnosis in the INBUILD trial: a randomised, double-blind, placebo-controlled, parallel-group trial

BACKGROUND

The INBUILD trial investigated the efficacy and safety of nintedanib versus placebo in patients with progressive fibrosing interstitial lung diseases (ILDs) other than idiopathic pulmonary fibrosis (IPF). We aimed to establish the effects of nintedanib in subgroups based on ILD diagnosis.

METHODS

The INBUILD trial was a randomised, double-blind, placebo-controlled, parallel group trial done at 153 sites in 15 countries. Participants had an investigator-diagnosed fibrosing ILD other than IPF, with chest imaging features of fibrosis of more than 10% extent on high resolution CT (HRCT), forced vital capacity (FVC) of 45% or more predicted, and diffusing capacity of the lung for carbon monoxide (DLco) of at least 30% and less than 80% predicted. Participants fulfilled protocol-defined criteria for ILD progression in the 24 months before screening, despite management considered appropriate in clinical practice for the individual ILD. Participants were randomly assigned 1:1 by means of a pseudo-random number generator to receive nintedanib 150 mg twice daily or placebo for at least 52 weeks. Participants, investigators, and other personnel involved in the trial and analysis were masked to treatment assignment until after database lock. In this subgroup analysis, we assessed the rate of decline in FVC (mL/year) over 52 weeks in patients who received at least one dose of nintedanib or placebo in five prespecified subgroups based on the ILD diagnoses documented by the investigators: hypersensitivity pneumonitis, autoimmune ILDs, idiopathic non-specific interstitial pneumonia, unclassifiable idiopathic interstitial pneumonia, and other ILDs. The trial has been completed and is registered with ClinicalTrials.gov, number NCT02999178.

FINDINGS

Participants were recruited between Feb 23, 2017, and April 27, 2018. Of 663 participants who received at least one dose of nintedanib or placebo, 173 (26%) had chronic hypersensitivity pneumonitis, 170 (26%) an autoimmune ILD, 125 (19%) idiopathic non-specific interstitial pneumonia, 114 (17%) unclassifiable idiopathic interstitial pneumonia, and 81 (12%) other ILDs. The effect of nintedanib versus placebo on reducing the rate of FVC decline (mL/year) was consistent across the five subgroups by ILD diagnosis in the overall population (hypersensitivity pneumonitis 73·1 [95% CI -8·6 to 154·8]; autoimmune ILDs 104·0 [21·1 to 186·9]; idiopathic non-specific interstitial pneumonia 141·6 [46·0 to 237·2]; unclassifiable idiopathic interstitial pneumonia 68·3 [-31·4 to 168·1]; and other ILDs 197·1 [77·6 to 316·7]; p=0·41 for treatment by subgroup by time interaction). Adverse events reported in the subgroups were consistent with those reported in the overall population.

INTERPRETATION

The INBUILD trial was not designed or powered to provide evidence for a benefit of nintedanib in specific diagnostic subgroups. However, its results suggest that nintedanib reduces the rate of ILD progression, as measured by FVC decline, in patients who have a chronic fibrosing ILD and progressive phenotype, irrespective of the underlying ILD diagnosis.

FUNDING

Boehringer Ingelheim.

Transfer of epinastine to infants through human breast milk

The purpose of this study was to develop an analytical method for analyzing epinastine in breast milk and maternal plasma samples to determine the safety of epinastine in breastfed infants. Six nursing mothers took epinastine hydrochloride (20 mg) once a day for 7 days, while a nursing mother took it for 30 days. Breast milk and blood samples were collected 2, 4, and 10 h after administration from the volunteers. A liquid chromatography-mass spectrometry system was used to analyze samples pretreated by liquid-liquid extractions. The concentration of epinastine in human milk was 10.3-33.5 ng/mL after 2 h, 9.1-63.8 ng/mL after 4 h, and 8.3-28.9 ng/mL after 10 h. The increase achieved 4 h after administration indicates that epinastine was transferred into human breast milk. However, the milk-to-plasma ratio had a wide range (0.82-3.39), while the relative infant dose at 4 h was 0.36-2.49%, which is lower than the safety level of transferability (10%). Moreover, the plasma levels of epinastine in two infants were slightly below the quantification limit. Overall, our results suggested that epinastine can safely be used by nursing mothers without affecting their infants.

P1032Efficacy and safety of radiofrequency catheter ablation for atrial fibrillation in patients undergoing hemodaialysis

Introduction

Although radiofrequency catheter ablation (RFCA) for atrial fibrillation (AF) has become a standard therapy, the ablation outcomes in patients undergoing hemodialysis (HD) has not been fully elucidated. The present study aimed to evaluate the clinical outcomes of RFCA for AF in patients undergoing HD.

Methods

Twenty-three patients undergoing HD (17 men, age 65±8 years, 19 paroxysmal AF) who underwent RFCA for drug-refractory AF in two institutes were enrolled in the study and defined as HD group. The clinical parameters, recurrence free rate and frequency of periprocedural complications were compared to 46 randomly selected age, gender and left atrial diameter matched controls not requiring HD defined as non-HD group (34men, age 67±7 years, 38 paroxysmal AF).

Results

The patients in HD group had a significantly lower body mass index (21±3 vs. 25±3 P<0.01), higher prevalence of coronary artery disease (30% vs. 10% P=0.04), and higher prevalence of congestive heart failure (52% vs. 10% P<0.01) compared to patients in non-HD group. Echocardiography indicated lower left ventricular ejection fraction (57±17% vs. 65±9% P=0.02), higher E/e' (20±8 vs. 12±4 P<0.01), higher tricuspid regurgitation pressure gradient (30mmHg vs. 24mmHg P<0.01) and more impaired left ventricular diastolic function in HD group. All the subjects underwent bilateral pulmonary vein isolation plus additional linear lesion. The number of ablation procedure was similar between the two groups (1.43±0.5 vs. 1.46±0.6 P=0.88). During the follow-up period of 37±25 months after the last procedure, the arrhythmia free rate was similar between the two groups (86% vs. 84% log-rank P=0.82). Vascular access complication occurred in two patients in HD group, and pericardial effusion occurred in one patient in non-HD group, while no life-threatening complications were observed in either group. Cardiogenic cerebral infarction occurred in one patient in non-HD group. Discontinuation of oral anticoagulation after the ablation was more often seen in the HD group compared to non-HD group (91% vs. 60% P<0.01).

Conclusions

Although patients undergoing HD had more impaired left ventricular systolic and diastolic function, RFCA for AF in patients with HD was shown to be as effective and safe as in non-HD patients. RFCA may be an efficient approach to manage AF in patients undergoing HD.

P2861Elevated cc chemokine receptor 2 expression and higher migratory activity of monocytes in atrial fibrillation patients with progressive structural remodeling

Background

Inflammation in atrial tissue underlies structural remodeling of left atrium, which is a hallmark of atrial fibrillation (AF). Activated monocytes mediate inflammation; however, the role of monocytes in AF pathogenesis has not been extensively examined. In this study, we thus investigated the association between structural remodeling of left atrium, represented by left atrial dimension (LAD), and characteristics of peripheral monocytes in patients with AF.

Methods

Blood samples were collected from patients undergone catheter ablation between July 2017 and October 2018, including AF patients (n=152) and paroxysmal supraventricular tachycardia (PSVT) patients, which serves as a control non-AF group (n=22). AF patients were further divided into two groups by the median of LAD (normal LAD group: LAD <40 mm, n=77, large LAD group: LAD ≥40 mm, n=75). Peripheral blood mononuclear cells (PBMC) were isolated to analyze monocyte subsets by flow cytometry. In a subset of patients, we further isolated monocytes from PBMC by using magnetic bead-based negative selection method then gene products associated with inflammation or monocyte functions were evaluated. We also examined migratory activity of monocytes toward monocyte chemotactic protein-1, a ligand for CC chemokine receptor 2 (CCR2), using a modified Boyden chamber method. Finally, we performed immunofluorescence staining of monocytes and macrophages in left atrial appendages resected from patients underwent coronary bypass graft surgery (CABG) complicated by AF.

Results

There were no differences in age, body mass index and high-sensitivity C-reactive protein levels among three groups, including non-AF, normal LAD and large LAD groups, except that more female subjects were included in non-AF group. We found that proportions of classical CD14++CD16- and nonclassical CD14+CD16++ monocytes were higher (non-AF: 71.2±7.3% vs. AF: 75.5±8.3%, p<0.05) and lower (non-AF: 16.4±5.9% vs. AF: 13.2±5.5%, p<0.05), respectively, in all AF patients compared with those in non-AF group, while no significant difference was observed between normal and large LAD groups. In monocytes from large LAD group, mRNA levels of CCR2, a receptor to mediate monocyte chemotaxis, were significantly higher compared to those in normal LAD group (Figure A, p<0.05). Furthermore, monocytes isolated from large LAD group exhibited higher migratory capacity compared to normal LAD group (Figure B, p<0.01). Finally, higher monocyte/macrophage infiltrations to left atrial appendages were implicated in patients with large LAD, shown by immunofluorescence staining.

Conclusions

Monocytes in AF patients with enlarged left atrium expressed higher CCR2 mRNA and were more active in chemotaxis to MCP-1, suggesting the proactive roles of activated monocytes in the pathogenesis of arterial remolding in AF.

P2848Electrical reconnections after pulmonary vein isolation with or without contact force-guided catheters: a comparison of the proficiency of atrial fibrillation ablation

Background

Atrial fibrillation (AF) ablation is the most commonly performed catheter ablation (CA) procedure today. The 2015 ACC/AHA/HRS Advanced Training Statement reported that the success rate of AF ablation is higher in high-volume centers than in low-volume centers. We tested whether the procedure proficiency of each operator was associated with the outcome of AF ablation, and whether the ablation outcome depended on whether contact force (CF)-guided catheters were used or not, in a high-volume center.

Methods

We conducted a retrospective observational study including all AF patients who underwent radiofrequency CA with or without CF support since 2016 at our hospital. The patients who underwent CA at other hospitals or underwent a balloon or surgical ablation in the first session were excluded. Each ipsilateral pulmonary vein (PV) pair was divided into 8 segments. The reconnection numbers and sites of the PV segment were evaluated in the second session. Operators were divided into the experienced group (≥100 AF cases/year, at least every 3 years) and developing group (other than the experienced group), respectively.

Results

Among 728 patients who underwent an initial AF ablation and were followed for 510±306 days, 131 (90 males, 65±10 years) received a second ablation procedure and were analyzed. A total of 260 and 264 PV isolations (PVI) were performed by the experienced and developing group operators in the initial ablation, respectively. Compared to the experienced group, the developing group had a longer procedure time for the PVI (35±15 vs. 28±10 min, p<0.001), higher frequency of reconnections of the PVs (73% vs. 59%, p=0.01) and higher number of reconnection gaps (2.1±2.0 vs. 1.5±2.0, p=0.02), respectively. There were no significantly differences in the number of gaps between the catheters with and without CF (1.6±2.0 vs. 1.4±2.0, p=0.65) in the experienced group, however, in the developing group a smaller total number of gaps (1.5±1.6 vs. 2.4±2.1, p=0.006) and less frequency reconnection gaps of the posterosuperior segment of the right PV (10% vs. 45%, p=0.005) were seen with catheters with CF than without. There was no significant difference in the procedure time for the PVI between catheters with and without CF.

Conclusions

The operator proficiency may predict the outcome after AF ablation even in high-volume centers. It is preferable to perform PVI with a CF-sensing catheter for operators without adequate proficiency.

Acknowledgement/Funding

JSPS KAKENHI Grant Number JP18K15865

P6337Prognostic impacts of serum uric acid levels in patients with chronic heart failure: insights from the CHART-2 Study

Background

Prognostic impact of serum uric acid (UA) levels in patients with heart failure (HF) remains to be fully elucidated, as previous studies were inconclusive with small study sample sizes. Furthermore, although the J-curve relationship between serum UA levels and cardiovascular events has been suggested in patients with hypertension and those with diabetes, it is still unclear whether this is also the case for patients with HF.

Purpose

We examined the prognostic impacts of serum UA levels in HF patients, using the database of our Chronic Heart Failure Registry and Analysis in the Tohoku district (CHART)-2 Study, the largest multicenter, prospective, observational cohort study for cardiovascular patients with HF or those at risk of HF in Japan (N=10,219).

Methods

First, we determined the cut-off value of serum UA levels at baseline by the Classification and Regression Tree (CART). Then, we divided 4,652 consecutive HF patients in the CHART-2 Study into 4 groups; G1 (<3.8 mg/dL, N=313), G2 (3.8–7.1 mg/dL, N=3,070), G3 (7.2–9.2 mg/dL, N=1,018), and G4 (≥9.3 mg/dL, N=251). Among the 4 groups, we compared clinical characteristics and incidence of all-cause death, HF hospitalization, and a composite of all-cause death and HF hospitalization.

Results

Mean age in G1, G2, G3, and G4 was 71±12, 69±12, 68±13, and 69±15 years, respectively (P<0.001). G1 was characterized by a significantly high prevalence of women as compared with G2, G3 and G4 (59, 32, 24 and 23%, respectively). Serum creatinine levels (0.8±0.4, 0.9±0.4, 1.2±0.6 and 1.4±0.8 mg/dL, respectively), prevalence of atrial fibrillation (34, 39, 45 and 50%, respectively), and diuretics use (36, 45, 67, 89%, respectively) increased from G1, G2, G3 to G4 (all P<0.001), while left ventricular ejection fraction decreased from G1, G2, G3 to G4 (59±15, 58±15, 54±15, and 52±17%, respectively, P<0.001). Median BNP levels were comparably low in G1 and G2 and then increased to G3 and G4 (94.4, 91.5, 130 and 192.5 pg/mL, respectively, P<0.001). As a HF etiology, prevalence of ischemic heart disease was highest in G2 and lowest in G4 (48, 52, 48, 38%, respectively, P<0.001), while that of dilated cardiomyopathy increased from G1, G2, G3 to G4 (11, 12, 16 and 20%, respectively, P<0.001). During the median follow-up period of 6.3 years, in G1, G2, G3 and G4, 111 (35%), 905 (29%), 370 (36%) and 139 (55%) patients died and 79 (25%), 729 (24%), 300 (29%) and 115 (46%) experienced HF hospitalization, respectively (both P<0.001). Cox proportional hazard models adjusted for clinical backgrounds showed that, as compared with G2, both G1 and G4 had increased risk for all-cause death, HF hospitalization and a composite of all-cause death, and HF hospitalization, indicating the J-curve relationship between serum UA levels and prognosis (Figure).

Prognostic impacts of serum UA levels

Conclusions

Both decreased and increased UA levels were associated with increased incidence of death and HF hospitalization in HF patients.

P924Prognostic significance of moderate primary mitral regurgitation and atrial fibrillation

Background

Severe primary mitral regurgitation [degenerativeMR (DMR)] is associated with poor outcome, including cardiac death and admission due to worsening heart failure. Whereas little information is available regarding the characteristics of moderate DMR and their impact on prognostic outcome.

The aim of the present study was to investigate the prognosis and its determinant in patients with moderate DMR.

Methods

From 13,700 consecutive patients who underwent transthoracic echocardiography. We selected moderate DMR but without other underlying cardiac diseases. Characteristics and event free rate as compared with age- and gender-matched patients with none to mild MR.

Results

Of a total of our cohort, 185 (1%) patients had moderate DMR, and we compared with 185 age- and gender-matched patients with none to mild MR. During the follow-up period of 1372±655 days, 30 patients (8%) met the composite endpoint defined as cardiac death and admission due to worsening heart failure. Kaplan-Meier analysis showed patients with moderate DMR was significantly associated with a poor outcome compared to patients with none to mild MR (log-ranktest P<0.0001). Cox proportional hazard ratio revealed thatmoderate MR and atrial fibrillation (AF) were the independent predictors of the composite endpoint.

Prgnostic outcome: AF and moderate DMR

Conclusions

Patients withmoderate DMR and concomitant AF had a significant poor outcome. An activesurveillance and some intervention for AF and moderate MR may be required.

P3767Progressive left atrial remodeling associates with cholesterol efflux capacity of HDL in atrial fibrillation patients

Background

The clinical significance of high-density lipoprotein (HDL) function, represented by cholesterol efflux capacity (CEC), in addition to serum HDL cholesterol (HDL-C) levels, has been recognized in the pathogenesis and prognosis in patients with atherosclerotic cardiovascular diseases. However, the roles of HDL in the development and the progression of atrial fibrillation (AF), has been rarely evaluated. In this study, we thus hypothesized that the compromised HDL function may be associated with the progression of pathological structural remodeling in left atrium (LA).

Objective

We explored the association between CEC of HDL and the left atrial dimension (LAD), a maker of structural remodeling in the LA, in patients with AF and control.

Methods

This is a single center case-control study including consecutive 260 AF patients (AF group) and 34 paroxysmal supraventricular tachycardia (PSVT) patients (PSVT group, served as a control group), who underwent catheter ablation from July 2017 to December 2018. Blood samples were collected before catheter ablation procedure. CEC of HDL was measured by using ex vivo radiotracer system that involved incubation of [3H] cholesterol-loaded J774.1 murine macrophage-like cells with apoB-depleted serum.

Results

Serum HDL-C level was lower in AF group compared to those of PSVT group (55.3±15.3mg/dl vs 61.7±13.3mg/dl: p=0.024). As a marker of HDL function, CEC of HDL was significantly lower in patients with AF group compared to those in PSVT patients (4.74±0.84% vs 5.20±0.99%: p=0.005, Fig 1). In all patients including both groups, CEC of HDL was inversely correlated with LAD (r=−0.25; p<0.001, Fig 2), indicating the inverse association between HDL function and the progression of structural remodeling in AF. Moreover, multivariate logistic regression analysis adjusted by age, gender, body mass index, ejection fraction, and HDL-C demonstrated that increase in CEC of HDL was associated with the lower risk to be highest quartiles of LAD (>42mm), even adjusted by serum HDL-C levels (odds ratio of 1-SD elevation in CEC of HDL for LAD>42mm: 0.63; 95% confidence interval: 0.40–0.97, p=0.037), which implicated the link between HDL function and progression of left atrial structural remodeling.

Conclusion

Findings in this study may suggest that compromised HDL functionality is associated with the pathogenesis of left atrial structural remodeling in AF patients.

Color change in Perlodel® tablets induced by LED lighting - photolysis of bromocriptine mesylate

Various types of fluorescent lights are found in the dispensing rooms of medical facilities, such as hospitals and pharmacies, in Japan. However, to reduce electric power consumption, it was necessary to evaluate the substitution of fluorescent lighting with light emitting diode (LED) lighting, which has become widespread in recent years. We subjectively evaluated several types of medicines stored under various light sources and found that different color changes were induced in tablets. In this study, we focused on Perlodel ® tablets, containing 2.5 mg bromocriptine mesylate, as an example for the objective evaluation of the differences in the color change of tablets when stored under LED lighting and fluorescent lighting. High-performance liquid chromatography (HPLC) analysis of part of the tablet surface area revealed a change from white to light brown or dark brown after 28 days of irradiation, with a residual concentration of bromocriptine mesylate of 85.5 % under fluorescent lighting, 85.6 % under daylight-color LED lighting, 90.3 % under bulb-color LED lighting, and 99.2 % in the dark. In addition, the ultraviolet (UV)-visible spectral study of the absorbance of a photo-product at 400-550 nm indicated that the color change of the Perlodel^® 2.5 mg tablet was caused by photochemical degradation of bromocriptine mesylate. Thus, this analysis of the photochemical changes in drugs stored under different light sources demonstrated the potency of LED lights. Through the objective evaluation of the color change, the cause of the color change was determined; this will allow us to develop a strategy that minimizes possible disadvantages to patients, such as a decrease in treatment efficacy owing to decomposition of the main component or adverse caused by decomposed matter.

Cytogenetic and agronomic characterization of intergeneric hybrids between Saccharum spp. hybrid and Erianthus arundinaceus

In sugarcane (Saccharum spp. hybrid) breeding, introgression of useful genes via intergeneric hybridization is a powerful strategy for improving the crop productivity. Erianthus arundinaceus shows great potential in terms of useful traits; however, little is known about the cytogenetic and agronomic characteristics of intergeneric hybrids between these two species. Here, we examine the cytogenetic and agronomic characteristics, and relationships between the two in intergeneric F₁ hybrids between modern sugarcane cultivar and E. arundinaceus identified by amplification of 5S rDNA markers and morphological characteristics. The nuclear DNA content of the hybrids varied from 6.07 to 8.94 pg/2C, with intra-clonal variation in DNA content and 5S rDNA sites. Genomic in situ hybridization revealed 53 to 82 chromosomes in the hybrids, with 53 to 56 derived from sugarcane and 1 to 29 from E. arundinaceus. There were significant positive correlations between the number of E. arundinaceus chromosomes and dry matter yield, millable stalk weight, single stalk weight, and stalk diameter, but not sucrose content, reducing sugar content, sucrose/reducing sugar ratio or fiber content. This detailed information on intergeneric F₁ hybrids between modern sugarcane cultivar and E. arundinaceus will contribute to effective utilization of E. arundinaceus in sugarcane breeding.

Luminal Na+ homeostasis has an important role in intestinal peptide absorption in vivo

Intestinal cell line studies indicated luminal Na⁺ homeostasis is essential for proton-coupled peptide absorption, because the driving force of PepT1 activity is supported by the apical Na⁺/H⁺ exchanger NHE3. However, there is no direct evidence demonstrating the importance of in vivo luminal Na⁺ for peptide absorption in animal experiments. To investigate the relationship between luminal Na⁺ homeostasis and peptide absorption, we took advantage of claudin 15-deficient (cldn15^-/-) mice, whereby Na⁺ homeostasis is disrupted. We quantitatively assessed the intestinal segment responsible for peptide absorption using radiolabeled nonhydrolyzable dipeptide (glycylsarcosine, Gly-Sar) and nonabsorbable fluid phase marker polyethylene glycol (PEG) 4000 in vivo. In wild-type (WT) mice, the concentration ratio of Gly-Sar to PEG 4000 decreased in the upper jejunum, suggesting the upper jejunum is responsible for peptide absorption. Gly-Sar absorption was decreased in the jejunum of cldn15^-/- mice. To elucidate the mechanism underlining these impairments, a Gly-Sar-induced short-circuit ( I_sc) current was measured. In WT mice, increments of Gly-Sar-induced I_sc were inhibited by the luminal application of a NHE3-specific inhibitor S3226 in a dose-dependent fashion. In contrast to in vivo experiments, robust Gly-Sar-induced I_sc increments were observed in the jejunal mucosa of cldn15^-/- mice. Gly-Sar-induced I_sc was inhibited by S3226 or a reduction of luminal Na⁺ concentration, which mimics low luminal Na⁺ concentrations in vivo . Our study demonstrates that luminal Na⁺ homeostasis is important for peptide absorption in native epithelia and that there is a cooperative functional relationship between PepT1 and NHE3. NEW & NOTEWORTHY Our study is the first to demonstrate that luminal Na⁺ homeostasis is important for proton-coupled peptide absorption in in vivo animal experiments.