Various studies have shown a role for citrulline as a gut mass biomarker in patients with short bowel syndrome. Our hypothesis is that plasma citrulline is both a gastrointestinal (GI) function and a gut mass marker. Our objective was to validate previous observations, by prospectively analyzing plasma citrulline concentrations in patients with GI disease with or without bowel resection, compared to patients without GI disease. Plasma from blood samples of parenteral nutrition fed neonates and infants was obtained. Samples were analyzed by ion-exchange chromatography. Data collected included age, diagnoses and surgical documentation of bowel resection. Patients were classified into 3 main groups: those without GI disease nor resection (Group 1), those with GI disease but no resection (Group 2), and those with GI disease and resection (Group 3). Group medians were compared using Kruskal-Wallis ANOVA. Seventeen samples were evaluated. Patients in Group 3 were older compared to patients in Groups 1 and 2; median age (in days) 156 vs. 12 vs. 57 respectively. Median (range) plasma citrulline concentrations were 20.9 (14.9 - 29.0) μmol/L, 8.7 (0.5 - 20.0) μmol/L and 9.6 (5.9 - 13.2) μmol/L for Groups 1, 2 and 3 respectively. There were significant differences among medians and sample distributions between Groups 1 and 2 and between 1 and 3 (p < 0.05). No differences were observed between Groups 2 and 3. Patients without GI disease and no resection had significantly higher plasma citrulline concentrations than patients with GI disease with or without resection at the time of assessment.
Citrulline is a non-essential amino acid synthesized predominantly in the enterocytes [
Our interest, as well as that of others, has been to evaluate plasma citrulline concentrations in premature infants and correlate those with their intestinal function [
Our study included neonates and infants up to 6 months of age, inpatients at Le Bonheur Children’s Hospital (LBCH) in Memphis, TN, who were enrolled in the PN service during their hospital stay and had received intravenous nutrition. All whole-blood samples had been collected as part of routine medical care. The samples were retrieved from the clinical laboratory at LBCH after routine analysis was completed. Blood samples were chosen based on available volume left, approximately 200 microliters required for chromatographic analysis. Once a sample had been identified for analysis, it was traced back to the patient whom it was extracted from. Data collected included age, diagnoses, surgical documentation of bowel resection if any, feeding regimens, and other notable routine-care laboratory values. They were classified into 3 main groups: patients without GI disease or resection (Group 1), patients with GI disease but no resection (Group 2), and patients with GI disease and resection (Group 3). The study was approved by the University of Tennessee Health Science Center (UTHSC) Institutional Review Board (IRB). The requirement for informed consent was waived by the IRB. Whole-blood was centrifuged and the supernatant was drawn into sampling tubes, discarding the buffy coat and erythrocytes. Plasma was analyzed by ion-exchange chromatography on a Prominence HPLC system (Shimadzu, Houston, TX) using a single- buffer (lithium citrate), two-temperature program with post-column ortho-phthalal- dehyde (OPA) derivatization and fluorescence detection (λEXC = 330 nm, λEM = 465 nm). Data were described as median with ranges, as they were not normally distributed. Nonparametric statistical analyses were used to compare group medians (Kruskal- Wallis ANOVA) performed on SPSS 32-bit software package for Windows (release 22.0.0; IBM Corp.).
We surveyed the clinical laboratory at LBCH daily between February and April 2012, searching for samples from patients that had been enrolled in the PN service. This study was a collection of retrospectively drawn blood samples in which citrulline concentrations were quantified prospectively. The total number of samples analyzed was seventeen, obtained from eleven different patients. Five samples forming Group 1, six in Group 2, and six in Group 3 (see
Patient | Sample | Age | Diagnoses | Type of Surgery | Bowel Resected (cm) | Feeding Regimen | Notable Lab Markers |
---|---|---|---|---|---|---|---|
A | 1 | 1 week | Esophageal Atresia/TEF | None | None | NPO | WBC: 16.7; CRP: 9.9 |
B | 1 | 3 months | Undiagnosed Congenital Syndrome | None | None | G-tube feeds at 150 mL/kg | WBC: 10.2; CRP: 6.2 |
C | 1 | 4 months | Ventricular/Atrial Septal Defect | Closure | None | Enteral Feeds at 100 mL/kg | WBC: 16.4; CRP: 48 |
D | 1 | 1 week | Persistent Pulmonary Hypertension/ ECMO | None | None | NPO | WBC: 5.2 |
2 | 2 weeks | Persistent Pulmonary Hypertension/ ECMO | None | None | NPO | WBC: 7.5 | |
E | 1 | 3 days | Duodenal Atresia | None | None | NPO | WBC: 13.4; CRP: <5 |
F | 1 | 2 months | Autoimmune Enteropathy | None | None | Oral feeds 45 mL/kg | WBC: 10.6 |
2 | 2 months | Autoimmune Enteropathy | None | None | Oral feeds 100 mL/kg | WBC: 7.3 | |
G | 1 | 4 months | MMIHS | None | None | Enteral feeds 22 mL/kg | WBC: 9.4 |
H | 1 | 3 weeks | Duodenal Atresia/ Midgut Volvulus | Exploratory Laparotomy | None | NPO | WBC: 11.3; CRP: 19.8 |
2 | 1 month | Duodenal Atresia/ Midgut Volvulus | Exploratory Laparotomy | None | NPO | WBC: 14.7; CRP: 8 | |
I | 1 | 4 months | Necrotizing Enterocolitis | Ex-lap, lysis of adhesions, end-to-end anastomosis | 45 cm jejunum | NPO | WBC: 29.4 |
2 | 5 months | Necrotizing Enterocolitis | Ex-lap, lysis of adhesions, end-to-end anastomosis | 45 cm jejunum | NPO | WBC: 39.1 | |
3 | 5 months | Necrotizing Enterocolitis | Ex-lap, lysis of adhesions, end-to-end anastomosis | 45 cm jejunum | NPO | WBC: 31.8 | |
4 | 5 months | Necrotizing Enterocolitis | Ex-lap with lysis of adhesions, end-to-end anastomosis | 45 cm jejunum | Tube feeds 6 mL/kg | WBC: 16.3 |
J | 1 | 4 months | Necrotizing Enterocolitis | Ex-lap, end-/ loop-jejunostomy and mucous fistula | 5 - 6 cm jejunum | NPO | NA |
---|---|---|---|---|---|---|---|
K | 1 | 6 months | Necrotizing Enterocolitis | Ex-lap, cecal stricturoplasty, anastomosis | 105 cm | NPO | WBC: 19.9 |
Tracheo-esophageal fistula (TEF), White blood cell count in ×103/µL (WBC), C-reactive protein in mg/L (CRP), nil per os (NPO), Extra-corporeal membrane oxygenation (ECMO), Megacystic Microcolon Intestinal Hypoperistalsis Syndrome (MMIHS), Not available (NA).
Our results suggest that patients without GI disease had significantly increased concentrations of citrulline in plasma compared to patients with GI disease, both with and without resection, as expected. The values in Group 1, which served as our control, are consistent with those reported in previous studies for premature infants [
There are limitations to this investigation that warrant further discussion. There was considerable variability in plasma citrulline, particularly in Group 2. This could be attributed to inherent analytical limitations from chromatography or ongoing intestinal disease. The assay is based on separation of citrulline from other plasma amino acids by ion-exchange chromatography as used in many studies by other research groups. The lowest concentration measurable from Stultz et al. was 4.2 µmol/L [
A few patients were receiving enteral feedings at the time the blood samples were collected. Though, secondary analyses revealed no significant difference in plasma citrulline concentrations when the cohort was divided as enterally fed or unfed. Sample size would have played a role as this was conditioned by our minimum volume requirement.
The most significant limitation, perhaps, is the use of one-time measurement of plasma citrulline in these patients. Gastrointestinal function is a dynamic process. In order to be described with any reliability, it would require having multiple assessments in order to understand any clinically-significant changes. With this study we improved upon two aspects of the previous investigation: first to prospectively analyze plasma citrulline concentrations from blood samples collected as part of routine patient care, and secondly, use enhanced analytical technology to improve sensitivity. If further validated, these findings would be clinically relevant for practitioners who could use it to better assess gastrointestinal function in patients and manage their transition from parenteral to oral/enteral feedings more appropriately.
Patients without GI disease had significantly higher plasma citrulline concentrations than patients with GI disease regardless of bowel resection. Evaluating plasma citrulline concentrations longitudinally in these same 3 categories of patients, during both a period of predominant parenteral nutrition and subsequent transition to enteral nutrition is critical to explore the potential use of citrulline as a surrogate marker of both gut mass and function.
The authors received financial support from the Children’s Foundation Research Institute and Le Bonheur Children’s Hospital (Acct# 65-0508), and the Center for Pediatric Pharmacokinetics and Therapeutics (CPPT).
Herrera, O.R., Storm, M.C. and Helms, R.A. (2016) Plasma Citrulline Concentrations in Neonates and Infants with or without Gastrointestinal Disease and Bowel Resection. Food and Nutrition Sci- ences, 7, 1063-1069. http://dx.doi.org/10.4236/fns.2016.712102