Plasma citrulline concentration: a reliable marker of small bowel absorptive capacity independent of intestinal inflammation

Citrulline levels following proximal versus distal small bowel resection

PURPOSE

Citrulline, a nonprotein amino acid synthesized by enterocytes, is a biomarker of bowel length and the capacity to wean from parenteral nutrition. However, the potentially variant effect of jejunal versus ileal excision on plasma citrulline concentration [CIT] has not been studied. This investigation compared serial serum [CIT] and mucosal adaptive potential after proximal versus distal small bowel resection.

METHODS

Enterally fed Sprague-Dawley rats underwent sham operation or 50% small bowel resection, either proximal (PR) or distal (DR). [CIT] was measured at operation and weekly for 8 weeks. At necropsy, histologic features reflecting bowel adaptation were evaluated.

RESULTS

By weeks 6-7, [CIT] in both resection groups significantly decreased from baseline (P<0.05) and was significantly lower than the concentration in sham animals (P<0.05). There was no difference in [CIT] between PR and DR at any point. Villus height and crypt density were higher in the PR than in the DR group (P≤0.02).

CONCLUSION

[CIT] effectively differentiates animals undergoing major bowel resection from those with preserved intestinal length. The region of intestinal resection was not a determinant of [CIT]. The remaining bowel in the PR group demonstrated greater adaptive potential histologically. [CIT] is a robust biomarker for intestinal length, irrespective of location of small intestine lost.

Intestinal adaptation following resection

Intestinal adaptation is a natural compensatory process that occurs following extensive intestinal resection, whereby structural and functional changes in the intestine improve nutrient and fluid absorption in the remnant bowel. In animal studies, postresection structural adaptations include bowel lengthening and thickening and increases in villus height and crypt depth. Functional changes include increased nutrient transporter expression, accelerated crypt cell differentiation, and slowed transit time. In adult humans, data regarding adaptive changes are sparse, and the mechanisms underlying intestinal adaptation remain to be fully elucidated. Several factors influence the degree of intestinal adaptation that occurs post resection, including site and extent of resection, luminal stimulation with enteral nutrients, and intestinotrophic factors. Two intestinotrophic growth factors, the glucagon-like peptide 2 analog teduglutide and recombinant growth hormone (somatropin), are now approved for clinical use in patients with short bowel syndrome (SBS). Both agents enhance fluid absorption and decrease requirements for parenteral nutrition (PN) and/or intravenous fluid. Intestinal adaptation has been thought to be limited to the first 1-2 years following resection in humans. However, recent data suggest that a significant proportion of adult patients with SBS can achieve enteral autonomy, even after many years of PN dependence, particularly with trophic stimulation.

Reduced plasma citrulline levels in low birth weight infants with necrotizing enterocolitis

BACKGROUND

Citrulline, a nonprotein amino acid, is an intermediate of the urea cycle and synthesized in small intestine. Lower plasma citrulline levels were associated with reduced function of enterocytes. Necrotizing enterocolitis (NEC) causes high morbidity and mortality, and leads impaired intestinal functions.

METHODS

Plasma citrulline levels of neonates with a gestational age <32 weeks and ≤1,500 gm who developed NEC stage II/III were measured by high-performance liquid chromatography.

RESULTS

We enrolled 36 preterm infants including 20 with NEC and 16 controls. Median citrulline levels of NEC and control groups were 8.6 and 20.18 μmol/l (P < 0.05), and cut off level of citrulline was 13.15 μmol/l with a sensitivity of 80% and a specificity of 82%. Median arginine levels of NEC and control groups were 22.02 and 39.89 μmol/l (P < 0.05), and cut off level of arginine was 28.52 μmol/l with a sensitivity of 70% and a specificity of 75%. Blood sampling day, gender, parenteral, and enteral nutrition did not affect the amino acid levels.

CONCLUSION

We found lower plasma citrulline and arginine levels in preterm infants with NEC. Further studies are needed to determine most appropriate levels to predict recovery and prognosis of NEC, and treatment options with these amino acids in preterm infants.

Correlations of plasma citrulline levels with clinical and endoscopic score and blood markers according to small bowel involvement in pediatric Crohn disease

OBJECTIVE

Several studies have indicated that plasma citrulline levels reflect the extent of mucosal injury of the small intestine. This study was performed to determine whether plasma citrulline levels correlate with the disease activity in pediatric patients with Crohn disease (CD).

METHODS

A total of 63 CD and 23 ulcerative colitis (UC) patients were included in this study. Disease severity was assessed by pediatric CD activity index (PCDAI), pediatric UC activity index, simplified endoscopic activity score for CD, C-reactive protein (CRP), and erythrocyte sedimentation rate (ESR). The correlations among these variables and plasma citrulline levels were evaluated. We performed subgroup analysis whether correlations between plasma citrulline levels and disease activity depend on small bowel involvement in patients with CD.

RESULTS

The plasma citrulline levels correlated negatively with CRP (r = -0.332, P = 0.008), ESR (r = -0.290, P = 0.022), and PCDAI (r = -0.424, P = 0.001) in patients with CD. The plasma citrulline levels were significantly lower in patients with jejunal involvement than in those without (P = 0.027). In subgroup analysis, patients with CD with jejunal involvement showed significantly negative correlations of plasma citrulline levels with CRP (r = -0.628, P = 0.016) and PCDAI (r = -0.632, P = 0.015); however, patients with CD without jejunal involvement revealed no correlations of plasma citrulline levels with CRP and PCDAI. There were no significant correlations between plasma citrulline levels and simplified endoscopic activity score for CD. There were no significant correlations of plasma citrulline levels with CRP, ESR, and pediatric UC activity index in patients with UC.

CONCLUSIONS

Plasma citrulline levels correlated with disease severity as measured by PCDAI, CRP, and ESR in pediatric patients with CD with jejunal involvement.

Non-invasive biological quantification of acute gastrointestinal graft-versus-host disease in children by plasma citrulline

Clinical grading of GI involvement during acute GVHD remains a challenging issue, especially in children. Plasma citrulline, a non-protein amino acid selectively produced and released by enterocytes, is a suitable surrogate endpoint for small intestinal epithelial cell mass, irrespective of the underlying cause of cell loss. Children referred for allogeneic bone marrow transplantation who were free from chronic malabsorption or constitutional disease involving the GI tract were consecutively included in this prospective study. Plasma citrulline and albumin concentration was measured every week between day 7 and day 28 of BMT until resolution of the aGVHD or occurrence of chronic GVHD. In total, 31 children were included between 2008 and 2011. After a CR, citrulline levels fell to a minimum level on day 7 and then increased to reach the initial value on day 28. After day 28, plasma citrulline but not albumin was strongly linked to the occurrence of GI GVHD, the threshold being set at 10 μmol/L. The correlation with clinical grade of GI-aGVHD now needs to be assessed in larger populations. In pediatric patients, citrulline is valuable as a suitable non-invasive marker of GI involvement in acute GVHD.

[Plasma citrulline concentration as a biomarker of intestinal function in short bowel syndrome and in intestinal transplant]

INTRODUCTION

Citrulline is a non-essential amino acid produced solely in the enterocyte. The aim of this study was to analyse the role of serum citrulline as a biomarker of enterocyte load in children with intestinal failure due to short bowel syndrome (SBS) and its relationship to enteral adaptation.

MATERIAL AND METHODS

Plasma citrulline concentration was determined by chromatography (normal value>15 μmol/L) in 57 patients (age 0.5-18 years) admitted to our Intestinal Rehabilitation Unit with intestinal failure. Those who were dehydrated, with renal insufficiency, or other conditions able to modify the results were excluded. Patients were divided into 4 groups: group i: SBS totally dependent on parenteral nutrition (PN); group ii: SBS under mixed enteral-parenteral nutrition; group iii: IF weaned from PN after a rehabilitation period; group iv: small bowel transplanted patients weaned from PN and taking a normal diet.

RESULTS

The mean ± SD plasma citrulline values were: group i (n=15): 7.1 ± 4.1; group ii (n=11): 15.8 ± 8.9; group iii (n=13): 20.6 ± 7.5; group iv (n=25): 28.8 ± 10.1. Values were significantly lower in group i in comparison with groups ii-iii-iv (P<.001), and in group ii in comparison with groups iii-iv (P<.001). A low citrulline was associated with remnant small bowel length (P<.001, r=0.85). In group iv citrulline levels decreased >50% in 3 patients who developed moderate-severe rejection, and in one patient who developed viral enteritis.

CONCLUSIONS

1. Plasma citrulline could be a sensitive and specific biomarker of the residual functional enterocyte load. 2. It is related to enteral feeding tolerance. 3. Its prognostic value in the process of intestinal adaptation and as a rejection marker in small bowel transplanted patients needs to be confirmed.

Plasma citrulline may be a good marker of intestinal functions in intestinal dysfunction

BACKGROUND

Plasma citrulline has been reported to be a good indicator of intestinal functional volume in patients with intestinal dysfunction. We reconfirmed the facts and also investigated the dynamic changes of plasma citrulline in acute-phase patients with intestinal dysfunction.

METHODS

We measured plasma citrulline in six patients with intestinal dysfunction who were in the acute and chronic phase for more than 6 months.

RESULTS

Four patients out of six could be withdrawn from total parenteral nutrition, and their plasma citrulline level dynamically changed according to their intestinal states and finally increased up to 15 nmol/mL. Two patients, who could not be withdrawn from parenteral nutrition, showed very low levels of plasma citrulline throughout the treatment course (under 15 nmol/mL).

CONCLUSION

The cut-off level of plasma citrulline indicating permanent intestinal dysfunction may be 15 nmol/mL in our data. In the acute phase, plasma citrulline changed dynamically according to the intestinal state and may be a good indicator of fluctuating intestinal functions. Thus, although only a few patients were enrolled in this study, plasma citrulline may be a good indicator of stable-state as well as acute-unstable-state intestinal functions.

Plasma citrulline concentration as a marker for disease activity in patients with Crohn's disease

BACKGROUND

Citrulline is a nitrogen end product produced from the intermediary metabolism of glutamine through the enzymatically mediated urea cycle, almost exclusively in the enterocytes of small intestinal epithelium, with some synthesis in colonocytes. Intestinal dysfunction resulting from intestinal diseases or injuries affects intermediary metabolism, which includes citrulline synthesis. We sought to determine whether plasma citrulline was a biomarker for disease activity in patients with Crohn's disease with the hypothesis that citrulline concentration would be reduced during active disease.

METHODS

A total of 81 outpatients aged 18 to 65 years (mean, 40.6±15.4 y) with a known history of Crohn's disease were studied prospectively. Patients with prior small intestinal resection, or renal or hepatic insufficiency were excluded. Crohn's disease activity was measured by Harvey-Bradshaw Index (HBI) and was correlated to the plasma citrulline concentration measured simultaneously (ion chromatography). Spearman correlation coefficients were used to assess for an association between the 2 variables. Subgroup analyses of patients with isolated small intestinal disease and endoscopically or radiologic verified disease activity were also performed.

RESULTS

Twenty-two patients had isolated colonic disease and 59 had small intestinal involvement. Twenty-six of these patients had concurrent endoscopy and/or computed tomography or magnetic resonance imaging. On the basis of HBI scores, 32 patients had active disease (HBI ≥5) and 49 patients had inactive disease. The mean HBI scores were 4.8±5.5. The mean plasma citrulline concentration was normal, although was below normal in some patients. However, it failed to distinguish between active and inactive patients based on the HBI (active 27.8±8.8 μmol/L, inactive 27.8±11.1 μmol/L, P=0.991). There was no significant linear association between the ranks of citrulline and ranks of HBI (rs=0.012, P=0.915). Of the 59 patients with isolated small intestinal disease, there was no association between plasma citrulline concentration and the HBI (Spearman correlation coefficient, 0.073; P=0.583). There was no difference in plasma citrulline concentrations among those with confirmed inflammation by imaging or endoscopy (confirmed, 26.2±11.8; negative, 28.0±10.0; independent t test P=0.583).

CONCLUSIONS

Plasma citrulline concentration was not a marker of disease activity in patients with Crohn's disease. However, all patients studied were outpatients and it is possible that plasma citrulline concentration may be depressed only in patients with more severe disease or extensive small bowel involvement. In addition, plasma citrulline may be increased in the postabsorptional state, and for the most part, our patients were nonfasting. More studies are needed to further elucidate the role of citrulline as a marker of disease activity in patients with Crohn's disease. The possibility also exists that citrulline may be a better marker in patients with previous resection, and this group will require specific evaluation.

Plasma citrulline as surrogate marker of intestinal inflammation in pediatric and adolescent with Crohn's disease: preliminary report

PURPOSE

Several researchers have found that plasma citrulline could be a marker of reduced enterocyte mass. The aim of this study was to assess the relationship between plasma citrulline and bowel inflammation and/or disease location in pediatric and adolescent Crohn's disease (CD) patients.

METHODS

Between January 2008 and January 2010, 31 CD patients and 44 controls were included in our study, and 15 out of the 31 CD patients continued a prospective survey. We evaluated the differences between groups, at baseline, in plasma citrulline and glutamine and between their baseline and final values during the prospective survey, and correlation between baseline values of citrulline and duration of disease, C-reactive protein, and fecal calprotectin.

RESULTS

Mean citrulline value was 33.0 ± 7.5 μmol/L in controls and 23.5 ± 8.4 μmol/L in CD patients (P < 0.0001). Plasma citrulline was significantly lower in patients with small bowel (SB) location than in patient with only ileo-colon disease (14.2 ± 5.5 and 24.7 ± 8.0, respectively; P = 0.0037). Citrulline ≤22 μmol/L reached sensitivity of 100% (95% confidence interval (CI) 54-100) and specificity of 98% (CI 89-99) in differentiating control subjects from CD with SB location.

CONCLUSIONS

CD patients have reduced concentration of plasma citrulline than controls. Intestinal damage rather than inflammation seems to be responsible for the reduced biosynthesis of citrulline, which decreases particularly in CD patients with SB location. This finding suggests the potential role of citrulline as marker of disease location, but future works will be needed to confirm this suggestion.

Low serum citrulline concentration correlates with catheter-related bloodstream infections in children with intestinal failure

BACKGROUND

Serum citrulline concentration is used as a biomarker of enterocyte mass and enteral tolerance, and low serum concentrations are correlated with bacteremia in immunosuppressed adults undergoing hematopoietic stem cell transplant. The authors sought to determine if citrulline was associated with the development of catheter-related bloodstream infections (CRBSIs) in children with intestinal failure.

METHODS

Data were reviewed from 66 children treated in a multidisciplinary intestinal rehabilitation program, who had serum concentration citrulline measured between January 2007 and August 2009. All patients had a diagnosis of intestinal failure requiring parenteral nutrition (PN) support. Exclusion criteria included central venous catheter in situ <30 days, creatinine clearance <20 mL/minute, or a history of organ transplant/immunosuppression.

RESULTS

A total of 15 patients were excluded because of the above criteria. In this cohort of 51 patients, 26 (51%) developed CRBSIs. Both groups were similar in terms of gestational age, diagnosis, nutrition status, and biochemical liver function tests. The mean (± standard deviation [SD]) minimum serum citrulline concentration was significantly lower in patients who developed CRBSIs (6.7 ± 4.6 µmol/L) than in those who did not (11.3 ± 6.4 µmol/L, P = .004). Multivariate logistic regression analysis identified lower minimum serum citrulline concentration and longer central venous catheter duration as independently associated with CRBSI (P = .003 and P = .038, respectively).

CONCLUSIONS

Low serum citrulline concentration and longer central venous catheter time are independently associated with CRBSI in children with intestinal failure. Serum citrulline concentration may be a useful biomarker to identify patients with intestinal failure who are at high risk of developing a CRBSI.

Oral citrulline does not affect whole body protein metabolism in healthy human volunteers: results of a prospective, randomized, double-blind, cross-over study

BACKGROUND & AIMS

Citrulline increases protein synthesis during refeeding in rodents with short bowel syndrome, aging and malnutrition, and improves nitrogen balance in fed healthy humans. The aim of the current study therefore was to determine whether citrulline had affected protein metabolism in healthy volunteers.

METHODS

In a randomized, double-blind, cross-over study, 12 healthy adults received a 5-h intravenous infusion of L-[1-(13)C]-leucine in the post-absorptive state, after a 7-day oral supplementation with 0.18 g/kg/day citrulline, or an iso-nitrogenous placebo. Treatment order was randomized, treatment periods were separated by 13-day wash out. Leucine appearance rate (Ra) was determined from plasma [1-(13)C]-keto-iso-caproate enrichment and leucine oxidation from expired (13)CO(2), and nitrogen balance was estimated from 6-h urinary urea excretion.

RESULTS

Compared with placebo, oral citrulline supplementation increased plasma citrulline, arginine and ornithine concentrations, but failed to affect albumin, transthyretin, free insulin and insulin-like growth factor (IGF)-1 plasma concentrations, urinary nitrate excretion, or nitrogen balance. Citrulline supplementation did not alter leucine Ra, leucine oxidation, nor whole-body protein synthesis.

CONCLUSION

In healthy, well nourished volunteers, oral citrulline increases plasma citrulline and arginine availability but does not affect whole-body protein kinetics in the post-absorptive state.

Glutamine, ornithine, citrulline and arginine levels in children with phenylketonuria: The diet effect

BACKGROUND

Phenylketonuria (PKU) therapeutic diet is characterized by the great replacement of natural protein with a phenylalanine-free formula.

AIM

To investigate the effect of diet on the amino acid serum levels in PKU patients and their total antioxidant status (TAS).

METHODS

Thirty-seven poorly controlled patients (group A), 43 patients who strictly adhered to their diet (group B) and 50 controls were included in the study. In patients and controls blood chemistry, TAS and serum amino acid level determinations were performed.

RESULTS

Phenylalanine levels significantly differed among the groups. Glutamine and ornithine levels were significantly higher in group A, while TAS (416±30 vs 228±23μmol/L, p<0.001), citrulline (39±15 vs 26±5μmol/L, p<0.001) and arginine levels (61±11 vs 80±12μmol/L, p<0.001) were higher in group B. The other determined amino acid serum levels did not differ among the groups of patients and controls.

CONCLUSIONS

The high glutamine and ornithine levels in group A may reflect the high natural protein intake. High phenylalanine levels in these patients may locally affect the hepatocyte, enterocyte, and/or renal function resulting in low citrulline and arginine levels contributing to their low TAS.

Assessment of Small Bowel Function in Critical Illness: Potential Role of Citrulline Metabolism

Small intestinal function in critically ill patients should ideally be assessed in order to determine the preferred feeding route, timing, and composition of enteral nutrition. Additionally, evaluation of small bowel function may lead to new insights aimed to maintain enterocyte integrity. Critically ill patients are likely to have impaired enterocyte function mainly as a consequence of diminished splanchnic blood flow associated with mucosal hyperpermeability and bacterial translocation, a pathological state believed to be pivotal in the development of sepsis and multiple organ dysfunction syndrome (MODS). However, feasible and validated clinical tools to reliably assess enterocyte function are lacking. This explorative review discusses the promising role of citrulline, a nonprotein amino acid almost exclusively generated by the enterocyte, as a biomarker reflecting enterocyte function in critically ill patients. Citrulline metabolism, its potential as enterocyte biomarker, and literature on citrulline in critically illness will be discussed. Finally, a novel test for enterocyte function, the citrulline generation test (enterocytic citrulline production upon stimulation with enteral or intravenous glutamine) will be considered briefly.

Acute intestinal failure in critically ill patients: is plasma citrulline the right marker?

INTRODUCTION

Small bowel functions are more complex than colon functions, and short bowel conditions are associated with increased mortality. Gastrointestinal dysfunction in critically ill patients is common, probably underestimated, and associated with a poor prognosis. However, a validated definition of acute intestinal failure is lacking, in absence of a marker to measure it. Consequently, small bowel dysfunction is not clearly integrated into the overall approach used to treat ICU patients.

MATERIALS AND METHODS

Review of the literature on gastrointestinal dysfunction in critically ill patients, and proposition of a definition of acute intestinal failure.

CONCLUSION

On the one hand, small bowel ischemia is related to acute reduction of enterocyte mass and loss of gut barrier function by epithelial lifting of villi. On the other hand, systemic inflammatory response syndrome (SIRS) and sepsis could be linked to an acute dysfunction of enterocytes without enterocyte reduction. Citrulline is an amino acid mainly synthesized by small bowel enterocytes. Various contexts of chronic and acute reduction of enterocyte mass have been correlated with low plasma citrulline concentration. Critically ill patients with shock have an acute reduction of enterocyte mass and reduced gut citrulline synthesis, leading to a low plasma citrulline concentration. Acute intestinal failure could be defined as an acute reduction of enterocyte mass and/or acute dysfunction of enterocytes, associated or not with loss of gut barrier function. The influence of SIRS and acute renal failure on plasma citrulline concentration and the value of this concentration as an indicator of acute intestinal failure in critically ill patients must be further evaluated.

Citrulline levels in a paediatric age group: does measurement on dried blood spots have additional value?

BACKGROUND

Citrulline is considered to be a marker of absorptive enterocyte mass. Citrulline levels can be measured in plasma or dried blood spot (DBS) samples. The purpose of this study is to calculate reference intervals for plasma and DBS citrulline concentrations in children and to examine the effect of age and gender.

METHODS

In 151 healthy subjects ranging from 1 month to 20 years of age, plasma and DBS citrulline concentration were determined by using Liquid Chromatography-tandem Mass Spectrometry. Citrulline concentrations were examined in relation to age and gender. Reference values were calculated according to the guidelines of the International Federation of Clinical Chemistry and the National Committee on Clinical Laboratory Standards.

RESULTS

No significant influence of age and gender could be discerned on plasma or DBS citrulline concentration. In children, the reference intervals for citrulline bounded by the 2.5 and 97.5 percentiles are 13.31-69.05 μmol/L and 23.70-49.04 μmol/L for plasma and DBS samples respectively.

CONCLUSIONS

The reference intervals for citrulline levels in healthy children are widely dispersed. Measuring citrulline concentrations in dried blood spots delivers no additional value to plasma measurements for the calculation of reference intervals in children.

Exploring a link between fatigue and intestinal injury during pelvic radiotherapy

BACKGROUND

The association between cancer-related fatigue and pathological processes in the body is largely unknown. This study was designed to investigate a possible linkage between fatigue and intestinal injury during pelvic radiotherapy.

METHODS

Twenty-nine women undergoing pelvic radiotherapy for anal or uterine cancer were prospectively followed. Fatigue and diarrhea were assessed using patient self-reported questionnaires. Plasma citrulline concentration, as a sign of intestinal injury, and C-reactive protein, orosomucoid, albumin, α(1)-antitrypsin, and haptoglobin, as signs of systemic inflammation, were analyzed.

RESULTS

Fatigue increased significantly (p < .001) and citrulline decreased significantly (p < .001) during treatment. A significant negative correlation (r = -0.40; p < .05) was found between fatigue and epithelial atrophy in the intestine (as assessed by plasma citrulline) after 3 weeks of treatment and a significant positive correlation (r = 0.75; p < .001) was found between fatigue and diarrhea. Signs of systemic inflammation were evident, with significant increases in serum orosomucoid, serum haptoglobin (p < .05) and serum α(1)-antitrypsin (p < .001) and a significant decrease in serum albumin (p < .001).

CONCLUSION

The present study indicates a link between fatigue and intestinal injury during pelvic radiotherapy. This observation should be considered as a preliminary finding because of the small sample size but may serve as a rationale for therapeutic interventions aimed at alleviating both fatigue and gastrointestinal symptoms during pelvic radiotherapy.

Simultaneous determination of l-citrulline and l-arginine in plasma by high performance liquid chromatography

OBJECTIVE

To develop a method for simultaneously determining l-citrulline and L-arginine levels in plasma using RP-HPLC with ultraviolet detection.

DESIGN AND METHODS

Plasma samples were deproteinized by trichloroacetic acid and heat. Phenyl-isothiocyanate (PITC) solution was used as derivatization reagent and a gradient elution was carried out.

RESULTS

The linearity for L-citrulline and L-arginine ranged from 0 to at least 1000 micromol/L. R(2) values were above 0.9999 for both. LODs for L-citrulline and L-arginine were 0.0201 micromol/L and 0.0476 micromol/L, respectively, while LOQs were 0.240 micromol/L and 0.448 micromol/L, respectively. Intra- and inter-day CVs were less than 3.40% and 7.2%, respectively. The average recovery was from 86.22% to 118.9%. L-citrulline and L-arginine concentrations in healthy controls were 60.77+/-9.18 micromol/L and 58.19+/-16.43 micromol/L, respectively.

CONCLUSION

This approach offers a reliable, efficient analytical platform for the simultaneous determination of citrulline and arginine levels in plasma.

Teduglutide, a novel mucosally active analog of glucagon-like peptide-2 (GLP-2) for the treatment of moderate to severe Crohn's disease

BACKGROUND

Teduglutide, an analog of glucagon-like peptide-2 (GLP-2), is associated with trophic effects on gut mucosa. Its role in the treatment of active Crohn's disease (CD) was assessed in a pilot, randomized, placebo-controlled, double-blinded, dose-ranging study.

METHODS

Subjects with moderate-to-severe CD were randomized 1:1:1:1 to placebo or 1 of 3 doses of teduglutide (0.05, 0.10, or 0.20 mg/kg daily) delivered as a daily subcutaneous injection for 8 weeks. The primary outcome measure was the percentage of subjects in each group that responded to treatment, defined as a decrease in Crohn's Disease Activity Index (CDAI) score to <150 or a decrease of > 100 points. At week 8 there was an optional 12-week open-label period of treatment with teduglutide 0.10 mg/kg/d.

RESULTS

One hundred subjects were enrolled and 71 completed the study. The mean baseline CDAI score was 290.8 +/- 57.6 and was similar across groups. There were numerically higher response and remission rates in all teduglutide-treated groups as compared with placebo, although the percentage of subjects who achieved a clinical response or remission was more substantial, and seen as early as week 2 of treatment in the highest dose (0.2 mg/kg/d) group (44% response and 32% remission versus 32% response and 20% remission in the placebo group). Of subjects who had not achieved remission during the 8-week placebo-controlled phase in the higher-dose group, 50% achieved remission during the more prolonged, open-label treatment phase. Plasma citrulline was similar across groups at baseline, but increased substantially over time in all teduglutide groups when compared with placebo at week 8. Adverse events were not different between placebo and active treatment groups.

CONCLUSIONS

Teduglutide is a novel and potentially effective therapy for inducing remission and mucosal healing in patients with active moderate-to-severe CD. Further clinical investigation of this growth factor is warranted.

Diagnosing malabsorption in the intensive care unit

Malabsorption as a result of decreased intestinal function is a frequently occurring problem in intensive care units. Small bowel dysfunction may lead to malnutrition and may predispose patients to infectious complications (sepsis) and may be linked to increased hospitalization duration, morbidity and mortality. There are several small bowel function tests, such as faecal fat excretion and sugar absorption tests, but data specifically applicable to the intensive care setting are limited. Moreover, there are multiple confounders such as altered intestinal permeability, changed transit time and renal dysfunction. A more specific test, fasting plasma citrulline concentration, has poor test characteristics for detection of decreased intestinal function in patients with dysfunctional enterocytes. Therefore, a citrulline generation test was recently developed in order to measure the conversion of glutamine (administered either enterally or intravenously) into citrulline. This conversion takes place exclusively in a properly functioning enterocyte; therefore, citrulline generation upon glutamine stimulation may be a promising biomarker for assessment of the small bowel function.

Plasma citrulline is a biomarker of enterocyte mass and an indicator of parenteral nutrition in HIV-infected patients

BACKGROUND

Plasma citrulline is a biomarker of enterocyte mass and function in humans.

OBJECTIVE

We evaluated citrulline in the reemerging context of diarrhea in HIV-infected patients receiving highly active antiretroviral therapy.

DESIGN

This study prospectively measured citrulline in 6 groups of HIV-1 patients (n = 115): 1) undetectable viral load without chronic diarrhea (a; n = 40) and with protease inhibitor-associated toxic chronic diarrhea (b; n = 26), 2) detectable viral load and CD4 > 200/mm(3) without (a; n = 6) and with (b; n = 11) chronic diarrhea, and 3) detectable viral load and CD4 <200/mm(3) without chronic diarrhea (a; n = 7) and with opportunistic intestinal infections or HIV enteropathy (b; n = 25). The influence of diarrhea on citrulline was assessed by comparing the a and b subgroups with healthy control subjects (n = 100).

RESULTS

Citrulline was slightly decreased (22-30 micromol/L) in groups 1b and 2b and was <22 micromol/L in 19 of 25 patients in group 3b. In group 3b, a citrulline concentration <10 micromol/L was associated with a clinical indication for parenteral nutrition (n = 6 of 8 compared with 2 of 17 if the citrulline concentration was >10 micromol/L; P < 0.05). Citrulline correlated positively with albumin (P < 0.01) and BMI (P < 0.05) and negatively with C-reactive protein (P < 0.01). When antiinfectious and nutritional therapies were successful (n = 18 of 25), citrulline normalized in 2-12 wk. Neither chronic hepatic or pancreatic disease nor lipodystrophy and the metabolic syndrome affected citrulline. Compared with control subjects (38 +/- 8 micromol/L), patients without chronic diarrhea (groups 1a, 2a, and 3a) had normal citrulline concentrations (36 +/- 6 micromol/L).

CONCLUSIONS

Plasma citrulline is a reliable biomarker of enterocyte functional mass in HIV patients. Citrulline does not allow the etiologic diagnosis of enteropathy, but it can discriminate between protease inhibitor toxic diarrhea and infectious enteropathy and quantify the functional consequences, which makes it an objective tool for indicating the need for parenteral nutrition.

Relationship between serum citrulline levels and progression to parenteral nutrition independence in children with short bowel syndrome

OBJECTIVE

Although bowel length is an important prognostic variable used in the management of children with short bowel syndrome (SBS), reliable measurements can be difficult to obtain. Plasma citrulline (CIT) levels have been proposed as surrogate markers for bowel length and function. We sought to evaluate the relationship between CIT and parenteral nutrition (PN) independence in children with SBS.

STUDY DESIGN

A retrospective chart review performed for all patients seen in a multidisciplinary pediatric intestinal rehabilitation clinic with a recorded CIT between January 2005 and December 2007 (n = 27).

RESULTS

Median age at time of CIT determination was 2.4 years. Diagnoses included necrotizing enterocolitis (26%), intestinal atresias (19%), and gastroschisis (22%). Citrulline levels correlated well with bowel length (R = 0.73; P < .0001) and was a strong predictor of PN independence (P Wilcoxon = 0.002; area under the receiver operating characteristic curve = 0.88; 95% confidence interval, 0.75-1.00). The optimal CIT cutoff point distinguishing patients who reached PN independence was 15 micromol/L (sensitivity = 89%; specificity = 78%).

CONCLUSION

Plasma CIT levels are strong predictors of PN independence in children with SBS and correlate well with a patient's recorded bowel length. A cutoff CIT level of 15 micromol/L may serve as a prognostic measure in counseling patients regarding the likelihood of future PN independence.

Long-term outcome of chronic intestinal pseudo-obstruction adult patients requiring home parenteral nutrition

OBJECTIVES

Chronic intestinal pseudo-obstruction (CIPO) is a rare, disabling disorder responsible for motility-related intestinal failure. Because it induces malnutrition, CIPO is a significant indication for home parenteral nutrition (HPN). The objective of the study was to evaluate long-term outcome of CIPO patients requiring HPN during adulthood.

METHODS

In total, 51 adult CIPO patients (18 men/33 women, median age at symptom occurrence 20 (0-74) years, 34/17 primary/secondary CIPO) followed up at our institution for HPN management between 1980 and 2006 were retrospectively studied for survival and HPN dependence rates using univariate and multivariate analysis.

RESULTS

Follow-up after diagnosis was 8.3 (0-29) years. Surgery was required in 84% of patients. The number of interventions was 3 +/- 3 per patient (mean +/- s.d.), leading to short bowel syndrome in 19 (37%) patients. Actuarial survival probability was 94, 78, 75, and 68% at 1, 5, 10, and 15 years, respectively. Multivariate analysis showed that lower mortality was associated with the ability to restore oral feeding at baseline (hazard ratio (HR) = 0.2 (0.06-0.65), P = 0.008) and symptom occurrence before the age of 20 years (HR=0.18 (0.04-0.88), P = 0.03). Higher mortality was associated with systemic sclerosis (HR=10.4 (1.6-67.9), P = 0.01). Actuarial HPN dependence was 94, 75, and 72% at 1, 2, and 5 years, respectively.

CONCLUSIONS

In this large cohort of CIPO adult patients with severe intestinal failure, i.e., those requiring HPN, we found a higher survival probability than previously reported. These results should be taken into account when considering intestinal transplantation.

Plasma citrulline measurement using UPLC tandem mass-spectrometry to determine small intestinal enterocyte pathology

Citrulline is a nonessential free amino acid, detectable in various biological fluids such as plasma, urine and cerebrospinal fluid. The plasma citrulline concentration is increasingly considered to be a reliable biomarker of enterocyte function. Current analysis usually involves lengthy HPLC separations as a part of classical amino acid profiling, or mass spectrometry usually in combination with derivatization. We employed UPLC-HILIC-tandem mass-spectrometry (MS/MS) of acetonitrile-derived supernatants from plasma samples of control subjects and of patients who had received myeloablative chemotherapy. Detection was achieved by the selected reaction monitoring of transitions: m/z 176-->70 and 180-->74 (for the deuterated standard), respectively. The method was precise and accurate with inter-day CV<3.9% (n=30), recoveries ranging from 98.0 to 100.3% and high linearity from 0.3 to at least 2,000 micromol/L. The results for 202 plasma samples agreed well with those obtained by the classical HPLC-fluorescence method. By a simple protein precipitation/extraction step and the UPLC separation the result can be available within 30 min of receipt with a capacity of at least 12 assays per hour. Citrulline in blood and plasma or serum was stable for at least 2 days at room temperature which would permit postal transport to the laboratory. The UPLC-MS/MS method for measuring plasma citrulline concentrations is fast and robust and is therefore an ideal tool for monitoring the intestinal enterocyte capacity of patients with various pathological conditions.

Measurement of nutrition status in Crohn's disease patients receiving infliximab therapy

AIM

There is limited information on the nutrition impact of antitumor necrosis factor-alpha treatment in adult Crohn's disease (CD). This study was performed to examine the effect of a 6-month course of infliximab on enterocyte function, nutrient status, metabolism, and body composition in these patients.

METHODS

Seven CD patients were assessed for disease activity, enterocyte function, and body composition prior to, after 6 weeks, and after 6 months of infliximab treatment. Measurements included (1) disease activity: Inflammatory Bowel Disease Questionnaire, Harvey Bradshaw Index, and C-reactive protein; (2) enterocyte function: folate, homocysteine, vitamin B(12), citrulline, vitamin D, beta-carotene, d-xylose absorption; (3) Prognostic Inflammatory and Nutritional Index (PINI); and (4) body composition and metabolism: body mass index (BMI), fat and lean body mass, resting energy expenditure (RRE), and respiratory quotient.

RESULTS

Most patients had improvement in disease activity with infliximab. PINI decreased in all patients (-3.35, P = .04). Plasma folate concentration significantly increased. There was an increase in BMI, fat mass, and lean body mass. The respiratory quotient increased in most patients. Changes in citrulline level and REE were inconsistent.

CONCLUSIONS

Crohn's disease patients have improvements in an index that measures both inflammation and nutrition (PINI) with infliximab therapy. Increases in plasma folate suggest improvement in enterocyte function and/or increased oral intake. The increase in respiratory quotient suggests decreased lipolysis and the lack of a starvation state. It was unclear whether weight gain was predominantly fat or lean muscle mass. These finding also support the use of PINI in Crohn's patients as an overall marker of inflammation and nutrition, and as a measure of response to infliximab therapy.

Systematic review: The evidence base for long-term management of coeliac disease

BACKGROUND

While gluten-free diet is an effective treatment for coeliac disease, the need for and goals of long-term management of patients are poorly defined.

AIM

To review systematically the complications and associations of coeliac disease, to identify potential risk factors, to define ways of assessing risk factors and to provide a strategy for management.

METHODS

Review of medical literature from 1975.

RESULTS

There is an increasing list of potential complications and/or conditions associated with coeliac disease, in particular, autoimmune disease, malignancy and bone disease. Risk factors that may predict or influence long-term outcomes include genetic susceptibility, environmental factors predominantly gluten ingestion, persistent small intestinal inflammation/injury and nutritional deficiencies. Genotyping of patients is yet to have an established clinical role in long-term management. Assessment of adherence to the gluten-free diet largely relies upon skilled dietary history, but the ultimate test is duodenal histopathology, which is the only currently established means of assessing healing. Symptoms, serology or other non-invasive means are poor predictors of healing and the likelihood of complications.

CONCLUSION

Evidence (albeit limited) that adherence to a gluten-free diet and mucosal healing prevent and/or ameliorate complications indicates that a planned long-term strategy for follow-up is essential.

Is serum citrulline measurement clinically useful in coeliac disease?

Citrulline (CIT), a non-protein amino acid in circulating blood, is almost exclusively contained in the enterocytes of small bowel mucosa and may represent a reliable marker of functioning enterocyte mass. The aim of this study was to evaluate the clinical utility of measuring serum citrulline levels in a group of patients affected by coeliac disease (CD). Fifty healthy volunteers, 21 patients with untreated coeliac disease and 6 patients with refractory coeliac disease took part in the study. Serum citrulline levels and duodenal lesions were evaluated at the time of diagnosis, and after at least 24 months of gluten-free diet. Serum citrulline concentrations were determined by ion exchange chromatography. In comparison to healthy volunteers, serum citrulline concentrations were significantly lower in untreated and refractory coeliac disease patients. No significant difference was found between untreated and refractory coeliac disease patients and between patients with different patterns of clinical presentation or various degrees of duodenal lesions. After a gluten-free diet, the mean of serum citrulline concentration was increased in all but one patient. Although, as expected, serum citrulline levels turned out to be low in coeliac disease, the clinical utility of their measurement is, at least, questionable in this condition.

The citrulline generation test: proposal for a new enterocyte function test

BACKGROUND

The amino acid citrulline is mainly produced by enterocytes from conversion of glutamine. As fasting plasma citrulline proved disappointing as a biomarker for enterocyte dysfunction in clinical practice, we propose a citrulline generation test (CGT) to assess enterocyte function.

AIM

To assess the feasibility of a CGT in healthy subjects and patients with decreased enterocyte mass.

METHODS

Nineteen healthy subjects, 16 patients with intestinal villous atrophy and nine patients with short bowel syndrome (SBS) were given an oral bolus of 20 g of the dipeptide alanine-glutamine. Subsequent changes in plasma citrulline and other amino acid concentrations were determined using reverse-phase high-performance liquid chromatography.

RESULTS

Following the oral bolus of alanine-glutamine, plasma citrulline concentrations showed a time dependent rise in healthy subjects of 44 +/- 13% (38-55 micromol/L, P < 0.0001). The slope from baseline plasma citrulline to peak concentrations was 0.22 +/- 0.08, 0.13 +/- 0.04 and 0.09 +/- 0.04 micromol/L/min in healthy subjects, patients with coeliac disease (CeD) and refractory CeD, respectively (healthy subjects vs. CeD P < 0.05, healthy subjects vs. refractory CeD P < 0.001). In patients with SBS, the CGT was able to distinguish between non-adapted and adapted SBS by means of the incremental area under the CGT curve till 90 min (iAUC T90). The iAUC T90 was 447 +/- 179 and 1039 +/- 178 micromol/L/min in non-adapted and adapted SBS, respectively (P = 0.04).

CONCLUSION

An oral bolus of alanine-glutamine induces a time-dependent rise in plasma citrulline concentration to an extent dependent on the existence of villous atrophy or enterocyte hyperplasia in CeD, and adapted SBS, respectively.

Citrulline as a biomarker of intestinal failure due to enterocyte mass reduction

BACKGROUND & AIMS

In human, citrulline (plasma concentration about 40 micromol/L) is an amino acid involved in intermediary metabolism and that is not incorporated in proteins. Circulating citrulline is mainly produced by enterocytes of the small bowel. For this reason plasma or serum citrulline concentration has been proposed as a biomarker of remnant small bowel mass and function. This article reviews this concept and its metabolic basis.

METHODS

Conditions in which there is a significantly reduced small bowel enterocyte mass and function and a plasma or serum citrulline were measured in adults and children. These studies included patients with a short bowel syndrome, villous atrophy states, Crohn's disease, during monitoring of digestive toxicity of chemotherapy and radiotherapy or follow-up of patients after small bowel transplantation.

RESULTS

In all these situations, with more than 500 studied patients a decreased level of plasma citrulline correlated with the reduced enterocyte mass independently of nutritional and inflammatory status. A close correlation between small bowel remnant length and citrullinemia was found. In addition, diagnosis of intestinal failure was assessed through plasma citrulline levels in severe small bowel diseases in which there is a marked enterocyte mass reduction.

DISCUSSION

The threshold for establishing a diagnosis of intestinal failure is lower in villous atrophy disease (10mumol/L) than in short bowel syndrome (20mumol/L). Compromised renal function is an important factor when considering plasma citrulline levels as a marker of intestinal failure as this potentially can increase circulating citrulline values.

CONCLUSIONS

Reduced plasma citrulline levels are an innovative quantitative biomarker of significantly reduced enterocyte mass and function in different disease states in humans.

Poor diagnostic accuracy of a single fasting plasma citrulline concentration to assess intestinal energy absorption capacity

OBJECTIVES

Our aim was to explore the diagnostic value of fasting citrulline concentrations to detect decreased intestinal energy absorption in patients with recently diagnosed celiac disease (CeD), refractory celiac disease (RCeD), and short bowel syndrome (SBS). Decreased intestinal energy absorption is regarded a marker of intestinal failure.

METHODS

Fasting plasma citrulline concentrations were determined by high performance liquid chromatography (HPLC) in a prospective study of 30 consecutive adult patients (15 CeD, 9 RCeD, and 16 SBS) and 21 healthy subjects. Intestinal energy absorption capacity using bomb calorimetry was determined in all patients and healthy subjects and was regarded as the gold standard for intestinal energy absorption function.

RESULTS

The mean fasting plasma citrulline concentration was lower in RCeD patients than in healthy subjects (28.5+/-9.9 vs 38.1+/-8.0 micromol/L, P<0.05) and CeD patients (28.5+/-9.9 vs 38.1+/-6.4 micromol/L, P<0.05), however, clearly within reference values. The mean intestinal energy absorption capacity was lower in SBS patients than in healthy subjects (64.3+/-18.2 vs 90.3+/-3.5%, P<0.001), CeD patients (64.3+/-18.2 vs 89.2+/-3.4%, P<0.001), and the RCeD group (64.3+/-18.2 vs 82.3+/-11.7%, P<0.01). No relation was observed between fasting plasma citrulline concentration and intestinal energy absorption capacity (Pearson r=0.09, P=0.56). The area under the ROC curve for fasting plasma citrulline to detect decreased intestinal energy absorption capacity (i.e., <85%) was 0.50.

CONCLUSION

Fasting plasma citrulline concentrations have poor test characteristics for detection of decreased intestinal energy absorption capacity in patients with enterocyte damage.

Citrulline and the gut

PURPOSE OF REVIEW

Citrulline, a nonprotein amino acid, is an important source of endogenous arginine. The gut is the main source of citrulline in humans. Hence, citrulline is a potential biomarker of short bowel function. Conversely, citrulline uptake by the gut is important for an oral supply of this amino acid as an alternative to arginine. This review discusses these two aspects of citrulline, as well as the recent developments in the understanding of its metabolism.

RECENT FINDINGS

Citrullinemia is such an efficient marker when the active mass of the bowel is affected that it can be used as a prognostic marker for parenteral nutrition weaning (if citrullinemia is >20 micromol/l) and as a factor for deciding between parenteral and enteral nutrition (as long as the pathology is considered). Citrullinemia should be used with care as a marker either of the intestinal absorption or following small bowel transplantation.

SUMMARY

Citrulline is easily taken up by the gut, with a broad set of transporters that can remove it from the lumen in the enterocytes. This is confirmed by pharmacokinetic studies and the efficacy is so great that oral complementation with citrulline seems more efficient than complementation with arginine to provide arginine.