L-citrulline improves splanchnic perfusion and reduces gut injury during exercise.

PURPOSE: Splanchnic hypoperfusion is a physiological phenomenon during strenuous exercise. It has been associated with gastrointestinal symptoms and intestinal injury and may hamper athletic performance. We hypothesized that L-citrulline supplementation improves splanchnic perfusion and decreases intestinal injury by enhancing arginine availability. The aim of this study was to determine the effect of L-citrulline intake on splanchnic perfusion, intestinal injury, and barrier function during exercise. METHODS: In this randomized, double-blind crossover study, 10 men cycled for 60 min at 70% of their maximum workload after L-citrulline (10 g) or placebo (L-alanine) intake. Splanchnic perfusion was assessed using gastric air tonometry. Sublingual microcirculation was evaluated by sidestream dark field imaging. Plasma amino acid levels and intestinal fatty acid binding protein concentrations, reflecting enterocyte damage, were assessed every 10 min. Urinary excretion of sugar probes was measured to evaluate intestinal permeability changes. RESULTS: Oral L-citrulline supplementation enhanced plasma citrulline (1840.3 ± 142.3 µM) and arginine levels (238.5 ± 9.1 µM) compared with that in placebo (45.7 ± 4.8 µM and 101.5 ± 6.1 µM, respectively, P < 0.0001), resulting in increased arginine availability. Splanchnic hypoperfusion was prevented during exercise after L-citrulline ingestion (reflected by unaltered gapg-apCO2 levels), whereas gapg-apCO2 increased with placebo treatment (P < 0.01). Accordingly, L-citrulline intake resulted in an increased number of perfused small sublingual vessels compared with that in placebo (7.8 ± 6.0 vs -2.0 ± 2.4, P = 0.06). Furthermore, plasma intestinal fatty acid binding protein levels were attenuated during exercise after L-citrulline supplementation compared with that in placebo (AUC0-60 min, -185% ± 506% vs 1318% ± 553%, P < 0.01). No significant differences were observed for intestinal permeability. CONCLUSIONS: Pre-exercise L-citrulline intake preserves splanchnic perfusion and attenuates intestinal injury during exercise in athletes compared with placebo, probably by enhancing arginine availability. These results suggest that oral L-citrulline supplementation is a promising intervention to combat splanchnic hypoperfusion-induced intestinal compromise.

Dietary protein digestion and absorption are impaired during acute postexercise recovery in young men.

Previously, we demonstrated that exercise can cause small intestinal injury, leading to loss of gut barrier function. The functional consequences of such exercise-induced intestinal injury on subsequent food digestion and absorption are unclear. The present study determined the impact of resistance-type exercise on small intestinal integrity and in vivo dietary protein digestion and absorption kinetics. Twenty-four young males ingested 20 g specifically produced intrinsically l-[1-(13)C]phenylalanine-labeled protein at rest or after performing a single bout of resistance-type exercise. Continuous intravenous infusions with l-[ring-(2)H5]phenylalanine were employed, and blood samples were collected regularly to assess in vivo protein digestion and absorption kinetics and to quantify plasma levels of intestinal fatty-acid binding protein (I-FABP) as a measure of small intestinal injury. Plasma I-FABP levels were increased after exercise by 35%, reaching peak values of 344 ± 53 pg/ml compared with baseline 254 ± 31 pg/ml (P < 0.05). In resting conditions, I-FABP levels remained unchanged. Dietary protein digestion and absorption rates were reduced during postexercise recovery when compared with resting conditions (P < 0.001), with average peak exogenous phenylalanine appearance rates of 0.18 ± 0.04 vs. 0.23 ± 0.03 mmol phenylalanine·kg lean body mass(-1)·min(-1), respectively. Plasma I-FABP levels correlated with in vivo rates of dietary protein digestion and absorption (rS = -0.57, P < 0.01). Resistance-type exercise induces small intestinal injury in healthy, young men, causing impairments in dietary protein digestion and absorption kinetics during the acute postexercise recovery phase. To the best of our knowledge, this is first evidence that shows that exercise attenuates dietary protein digestion and absorption kinetics during acute postexercise recovery.

Novel multi-sugar assay for site-specific gastrointestinal permeability analysis: a randomized controlled crossover trial.

BACKGROUND & AIMS: Increased gastrointestinal (GI) permeability is an important hallmark of many conditions, potentially leading to antigen exposure and sepsis. Current permeability tests are hampered by analytical limitations. This study aims to compare the accuracy of our multi-sugar (MS) and the classical dual sugar (DS) test for detection of increased GI permeability. METHODS: Ten volunteers received permeability analysis using MS (1 g sucrose, lactulose, sucralose, erythritol, 0.5 g rhamnose in water) or DS (5 g lactulose, 0.5 g rhamnose), after indomethacin or placebo. Blood and urine were analyzed by isocratic LC-MS. RESULTS: MS testing revealed significantly elevated urinary lactulose/rhamnose (L/R) ratios after indomethacin, due to enhanced lactulose excretion (P < .01) and unaltered rhamnose excretion. The DS test showed increased L/R ratios, due to increased lactulose excretion and decreased rhamnose excretion (both P < .05). After indomethacin, plasma L/R increased in both assays (P < .05 and P < .01). Urinary and plasma L/R ratios correlated significantly. Indomethacin increased sucrose excretion and 0-1 h sucrose/rhamnose. Colon permeability was unchanged. CONCLUSIONS: Sensitive permeability analysis is feasible in plasma and urine using MS or DS test. In contrast to the DS test, monosaccharide excretion is not decreased by the MS test. In short, the MS test provides accurate, site-specific information on gastroduodenal, small, and large intestinal permeability. Registered at US National Library of Medicine (http://www.clinicaltrials.gov, NCT00943345).

Polyethylene glycol versus dual sugar assay for gastrointestinal permeability analysis: is it time to choose?

BACKGROUND: Increased intestinal permeability is an important measure of disease activity and prognosis. Currently, many permeability tests are available and no consensus has been reached as to which test is most suitable. The aim of this study was to compare urinary probe excretion and accuracy of a polyethylene glycol (PEG) assay and dual sugar assay in a double-blinded crossover study to evaluate probe excretion and the accuracy of both tests. METHODS: Gastrointestinal permeability was measured in nine volunteers using PEG 400, PEG 1500, and PEG 3350 or lactulose-rhamnose. On 4 separate days, permeability was analyzed after oral intake of placebo or indomethacin, a drug known to increase intestinal permeability. Plasma intestinal fatty acid binding protein and calprotectin levels were determined to verify compromised intestinal integrity after indomethacin consumption. Urinary samples were collected at baseline, hourly up to 5 hours after probe intake, and between 5 and 24 hours. Urinary excretion of PEG and sugars was determined using high-pressure liquid chromatography-evaporative light scattering detection and liquid chromatography-mass spectrometry, respectively. RESULTS: Intake of indomethacin increased plasma intestinal fatty acid-binding protein and calprotectin levels, reflecting loss of intestinal integrity and inflammation. In this state of indomethacin-induced gastrointestinal compromise, urinary excretion of the three PEG probes and lactulose increased compared with placebo. Urinary PEG 400 excretion, the PEG 3350/PEG 400 ratio, and the lactulose/rhamnose ratio could accurately detect indomethacin-induced increases in gastrointestinal permeability, especially within 2 hours of probe intake. CONCLUSION: Hourly urinary excretion and diagnostic accuracy of PEG and sugar probes show high concordance for detection of indomethacin-induced increases in gastrointestinal permeability. This comparative study improves our knowledge of permeability analysis in man by providing a clear overview of both tests and demonstrates equivalent performance in the current setting.

Aggravation of exercise-induced intestinal injury by Ibuprofen in athletes.

INTRODUCTION: Nonsteroidal anti-inflammatory drugs are commonly used by athletes to prevent anticipated exercise-induced pain, thereby putatively improving physical performance. However, these drugs may have potentially hazardous effects on the gastrointestinal (GI) mucosa during strenuous physical exercise. The aim of the current study was to determine the effect of oral ibuprofen administration before exercise on GI integrity and barrier function in healthy individuals. METHODS: Nine healthy, trained men were studied on four different occasions: 1) 400 mg ibuprofen twice before cycling, 2) cycling without ibuprofen, 3) 400 mg ibuprofen twice at rest, and 4) rest without ibuprofen intake. To assess small intestinal injury, plasma intestinal fatty acid binding protein (I-FABP) levels were determined, whereas urinary excretion of orally ingested multisugar test probes was measured using liquid chromatography and mass spectrometry to assess GI permeability. RESULTS: Both ibuprofen consumption and cycling resulted in increased I-FABP levels, reflecting small intestinal injury. Levels were higher after cycling with ibuprofen than after cycling without ibuprofen, rest with ibuprofen, or rest without ibuprofen (peak I-FABP, 875 ± 137, 474 ± 74, 507 ± 103, and 352 ± 44 pg·mL, respectively, P < 0.002). In line, small intestinal permeability increased, especially after cycling with ibuprofen (0-2 h urinary lactulose/rhamnose ratio, 0.08 (0.04-0.56) compared with 0.04 (0.00-0.20), 0.05 (0.01-0.07), and 0.01 (0.01-0.03), respectively), reflecting loss of gut barrier integrity. Interestingly, the extent of intestinal injury and barrier dysfunction correlated significantly (RS = 0.56, P < 0.001). CONCLUSION: This is the first study to reveal that ibuprofen aggravates exercise-induced small intestinal injury and induces gut barrier dysfunction in healthy individuals. We conclude that nonsteroidal anti-inflammatory drugs consumption by athletes is not harmless and should be discouraged.

Physiology and pathophysiology of splanchnic hypoperfusion and intestinal injury during exercise: strategies for evaluation and prevention.

Physical exercise places high demands on the adaptive capacity of the human body. Strenuous physical performance increases the blood supply to active muscles, cardiopulmonary system, and skin to meet the altered demands for oxygen and nutrients. The redistribution of blood flow, necessary for such an increased blood supply to the periphery, significantly reduces blood flow to the gut, leading to hypoperfusion and gastrointestinal (GI) compromise. A compromised GI system can have a negative impact on exercise performance and subsequent postexercise recovery due to abdominal distress and impairments in the uptake of fluid, electrolytes, and nutrients. In addition, strenuous physical exercise leads to loss of epithelial integrity, which may give rise to increased intestinal permeability with bacterial translocation and inflammation. Ultimately, these effects can deteriorate postexercise recovery and disrupt exercise training routine. This review provides an overview on the recent advances in our understanding of GI physiology and pathophysiology in relation to strenuous exercise. Various approaches to determine the impact of exercise on the individual athlete's GI tract are discussed. In addition, we elaborate on several promising components that could be exploited for preventive interventions.

Exercise-induced splanchnic hypoperfusion results in gut dysfunction in healthy men.

BACKGROUND: Splanchnic hypoperfusion is common in various pathophysiological conditions and often considered to lead to gut dysfunction. While it is known that physiological situations such as physical exercise also result in splanchnic hypoperfusion, the consequences of flow redistribution at the expense of abdominal organs remained to be determined. This study focuses on the effects of splanchnic hypoperfusion on the gut, and the relationship between hypoperfusion, intestinal injury and permeability during physical exercise in healthy men. METHODS AND FINDINGS: Healthy men cycled for 60 minutes at 70% of maximum workload capacity. Splanchnic hypoperfusion was assessed using gastric tonometry. Blood, sampled every 10 minutes, was analyzed for enterocyte damage parameters (intestinal fatty acid binding protein (I-FABP) and ileal bile acid binding protein (I-BABP)). Changes in intestinal permeability were assessed using sugar probes. Furthermore, liver and renal parameters were assessed. Splanchnic perfusion rapidly decreased during exercise, reflected by increased gap(g-a)pCO(2) from -0.85±0.15 to 0.85±0.42 kPa (p<0.001). Hypoperfusion increased plasma I-FABP (615±118 vs. 309±46 pg/ml, p<0.001) and I-BABP (14.30±2.20 vs. 5.06±1.27 ng/ml, p<0.001), and hypoperfusion correlated significantly with this small intestinal damage (r(S) = 0.59; p<0.001). Last of all, plasma analysis revealed an increase in small intestinal permeability after exercise (p<0.001), which correlated with intestinal injury (r(S) = 0.50; p<0.001). Liver parameters, but not renal parameters were elevated. CONCLUSIONS: Exercise-induced splanchnic hypoperfusion results in quantifiable small intestinal injury. Importantly, the extent of intestinal injury correlates with transiently increased small intestinal permeability, indicating gut barrier dysfunction in healthy individuals. These physiological observations increase our knowledge of splanchnic hypoperfusion sequelae, and may help to understand and prevent these phenomena in patients.

Novel analytical approach to a multi-sugar whole gut permeability assay.

Many pathophysiological conditions are associated with increased gastrointestinal permeability, reflecting an elevated risk of endotoxaemia, inflammation, and sepsis. Permeability tests are increasingly used in clinical practice to obtain information on gastrointestinal functioning, but tests are often restricted to the small intestine, and require large oral sugar doses. Therefore, a novel multi-sugar assay was developed, allowing assessment of whole gut permeability changes in urinary and plasma samples collected at regular intervals from 10 healthy volunteers at baseline and after intake of monosaccharides (rhamnose and erythritol) and disaccharides (sucrose, lactulose, and sucralose). Samples were analyzed by isocratic cation-exchange LC-MS. Sample preparation and detection conditions were optimized. After centrifugation, chromatographic separation was achieved on an IOA-1000 column set at 30°C. Column effluent was mixed with ammonia for sugar-ammonium adduct formation. The lower limit of detection was 0.05 µmol/L for disaccharides and 0.1 µmol/L for monosaccharides. Linearity for each probe was between 1 and 1000 µmol/L (R(2): 0.9987-0.9999). Coefficients of variation were <5% in urine, and <9% in plasma. Recovery data were within the 90% to 110% range at all spiked concentrations. This highly sensitive novel LC-MS approach resulted in a significant decrease of the detection limit for all sugar probes, allowing a 5-fold reduction of the commonly used lactulose dose and the addition of sugar probes to also assess the gastroduodenal and colon permeability. In combination with its extended application in plasma, these features make the novel assay a promising tool in the assessment of site-specific changes in gastrointestinal permeability in clinical practice.

Early diagnosis of intestinal ischemia using urinary and plasma fatty acid binding proteins.

OBJECTIVE: This study aims at improving diagnosis of intestinal ischemia, by measuring plasma and urinary fatty acid binding protein (FABP) levels. METHODS: Fifty consecutive patients suspected of intestinal ischemia were included and blood and urine were sampled at time of suspicion. Plasma and urinary concentrations of intestinal FABP (I-FABP), liver FABP (L-FABP) and ileal bile acid binding protein (I-BABP) were measured using enzyme-linked immunosorbent assays. RESULTS: Twenty-two patients suspected of intestinal ischemia were diagnosed with intestinal ischemia, 24 patients were diagnosed with other diseases, and 4 patients were excluded from further analysis fulfilling exclusion criteria. Median plasma concentrations of I-FABP and L-FABP and urinary concentrations of all 3 markers were significantly higher in patients with proven intestinal ischemia than in patients suspected of intestinal ischemia with other final diagnoses (plasma I-FABP; 653 pg/mL vs. 109 pg/mL, P = 0.02, plasma L-FABP; 117 ng/mL vs. 25 ng/mL, P = 0.006, urine I-FABP; 3377 pg/mL vs. 115 pg/mL, P = 0.001, urine L-FABP; 1,199 ng/mL vs. 37 ng/mL, P =0.004, urine I-BABP; 48.6 ng/mL vs. 0.6 ng/mL, P = 0.002). Positive and negative likelihood ratios significantly increased positive posttest probability and decreased negative posttest probability on intestinal ischemia. In patients with intestinal ischemia a trend to higher plasma I-BABP levels was observed when the ileum was involved (18.4 ng/mL vs. 2.9 ng/mL, P = 0.05). CONCLUSION: Plasma and especially urinary I-FABP and L-FABP levels and urinary I-BABP levels can improve early diagnosis of intestinal ischemia. Furthermore, plasma I-BABP levels can help in localizing ileal ischemia.

Non-invasive markers for early diagnosis and determination of the severity of necrotizing enterocolitis.

OBJECTIVES: To improve diagnosis of necrotizing enterocolitis (NEC) by noninvasive markers representing gut wall integrity loss (I-FABP and claudin-3) and gut wall inflammation (calprotectin). Furthermore, the usefulness of I-FABP to predict NEC severity and to screen for NEC was evaluated. METHODS: Urinary I-FABP and claudin-3 concentrations and fecal calprotectin concentrations were measured in 35 consecutive neonates suspected of NEC at the moment of NEC suspicion. To investigate I-FABP as screening tool for NEC, daily urinary levels were determined in 6 neonates who developed NEC out of 226 neonates included before clinical suspicion of NEC. RESULTS: Of 35 neonates suspected of NEC, 14 developed NEC. Median I-FABP, claudin-3, and calprotectin levels were significantly higher in neonates with NEC than in neonates with other diagnoses. Cutoff values for I-FABP (2.20 pg/nmol creatinine), claudin-3 (800.8 INT), and calprotectin (286.2 microg/g feces) showed clinically relevant positive likelihood ratios (LRs) of 9.30, 3.74, 12.29, and negative LRs of 0.08, 0.36, 0.15, respectively. At suspicion of NEC, median urinary I-FABP levels of neonates with intestinal necrosis necessitating surgery or causing death were significantly higher than urinary I-FABP levels in conservatively treated neonates. Of the 226 neonates included before clinical suspicion of NEC, 6 developed NEC. In 4 of these 6 neonates I-FABP levels were not above the cutoff level to diagnose NEC before clinical suspicion. CONCLUSIONS: Urinary I-FABP levels are not suitable as screening tool for NEC before clinical suspicion. However, urinary I-FABP and claudin-3 and fecal calprotectin are promising diagnostic markers for NEC. Furthermore, urinary I-FABP might also be used to predict disease severity.