Correlates of Plasma Citrulline, a Potential Marker of Enterocyte Mass, among Children with Stunting: A Cross-Sectional Study in Uganda

BACKGROUND

Environmental enteric dysfunction (EED) is associated with stunting. Citrulline, produced in mature enterocytes, may be a valuable biomarker of small intestinal enterocyte mass in the context of EED.

OBJECTIVES

We aimed to explore the correlates of plasma citrulline (p-cit) in children with stunting.

METHODS

In a cross-sectional study using baseline data from the community-based MAGNUS (milk affecting growth, cognition and the gut in child stunting) trial (ISRCTN13093195), we explored potential correlates of p-cit in Ugandan children with stunting aged 12-59 mo. Using linear regression in univariate and multivariate models, we explored associations with socioeconomics, diet, micronutrient status, and water, sanitation, and hygiene characteristics. The influence of covariates age, fasting, and systemic inflammation were also explored.

RESULTS

In 750 children, the mean ± standard deviation age was 32.0 ± 11.7 mo, and height-for-age z-score was -3.02 ± 0.74. P-cit, available for 730 children, differed according to time fasted and was 20.7 ± 8.9, 22.3 ± 10.6 and 24.2 ± 13.1 μmol/L if fasted <2, 2-5 and >5 h, respectively. Positive correlates of p-cit were age [0.07; 95% confidence interval (CI): 0.001, 0.15 μmol/L] and log10 serum insulin-like growth factor-1 (8.88; 95% CI: 5.09, 12.67 μmol/L). With adjustment for systemic inflammation, the association with serum insulin-like growth factor-1 reduced (4.98; 95% CI: 0.94, 9.03 μmol/L). Negative correlates of p-cit included food insecurity, wet season (-3.12; 95% CI: -4.97, -1.26 μmol/L), serum C-reactive protein (-0.15; 95% CI: -0.20, -0.10 μmol/L), serum α1-acid glycoprotein (-5.34; 95% CI: -6.98, -3.70 μmol/L) and anemia (-1.95; 95% CI: -3.72, -0.18 μmol/L). Among the negatively correlated water, sanitation, and hygiene characteristics was lack of soap for handwashing (-2.53; 95% CI: -4.82, -0.25 μmol/L). Many associations attenuated with adjustment for inflammation.

CONCLUSIONS

Many of the correlates of p-cit are characteristic of populations with a high EED prevalence. Systemic inflammation is strongly associated with p-cit and is implicated in EED and stunting. Adjustment for systemic inflammation attenuates many associations, reflecting either confounding, mediation, or both. This study highlights the complex interplay between p-cit and systemic inflammation.

Bile acid-farnesoid X receptor-fibroblast growth factor 19 axis in patients with short bowel syndrome: The randomized, glepaglutide phase 2 trial

BACKGROUND

The gut-liver axis and enterohepatic circulation have gained increasing attention lately. Patients with short bowel syndrome (SBS) are, in fact, human knock-out models that may assist in the understanding of bile acid synthesis and regulation. We evaluated effect of glepaglutide (a long-acting glucagon-like peptide-2 analog) on bile acid synthesis (the enterohepatic circulation of bile acids and liver biochemistry in patients with SBS).

METHOD

In a single-center, double-blinded, dose-finding, crossover phase 2 trial, 18 patients with SBS were randomly assigned to 2 of 3 treatment arms (0.1, 1, and 10 mg) with daily subcutaneous injections of glepaglutide for 3 weeks. The washout period between the 2 treatment periods was 4-8 weeks. Measurements were performed at baseline and at the end of each treatment period and included postprandial plasma samples for fibroblast growth factor 19 (FGF19), 7α-hydroxy-4-cholesten-3-one (C4), total excretion of fecal bile acids, gene expression of farnesoid X receptor (FXR) in intestinal mucosal biopsies, total plasma bile acids, and liver biochemistry.

RESULTS

Compared with baseline, the median (interquartile range) postprandial response (area under the curve 0-2h) of FGF19 increased by 150 h × ng/L (41, 195; P = 0.001) and C4 decreased by 82 h × µg/L (-169, -28; p = 0.010) in the 10-mg dose. FXR gene expression did not change in any of the groups. Alkaline phosphatase significantly decreased.

CONCLUSION

Glepaglutide may stimulate the bile acid/FXR/FGF19 axis, leading to increased plasma concentrations of FGF19. Thereby, glepaglutide may ameliorate the accelerated de novo bile acid synthesis and play a role in the prevention and/or treatment of intestinal failure-associated liver disease.

Plasma citrulline is not a biomarker for intestinal adaptation in short bowel syndrome, studied in piglets: a model for human neonates

BACKGROUND

There are no in vivo methods to measure adaptation in neonatal short bowel syndrome (SBS). We evaluated citrulline (Cit) levels in neonatal piglet surgical models of SBS.

METHODS

Piglets underwent 75% mid-intestinal resection with jejunoileal anastomosis (JI), 75% distal resection of ileum with jejunocolic anastomosis (JC) or sham surgery. Jugular and gastric catheters were inserted for parenteral and enteral nutrition. On D7, small intestine length and weight were measured, jejunum collected for histopathology and Cit level determined.

RESULTS

JI (n = 5) compared to JC (n = 5) had increased small intestinal length (JC - 17.5 cm; JI +22.0 cm; p = 0.02) and mass (JC 43.1 mg/cm/kg; JI 51.3 mg/cm/kg; p = 0.02), while Cit did not differ (JI 801.0 µM; JC 677.7 µM; p = 0.90). Including non-resected shams (n = 4), Cit correlated with length (R² = 0.48; p = 0.006), but not for SBS alone (R² = 0.11; p = 0.4), mass (R² = 0.05; p = 0.5). A second experiment compared change in Cit levels from baseline to D7. Levels declined in sham (n = 8) and JC (n = 10) (sham - 110.1 µM; JC - 56.6 µM; p = 0.17), regardless of intestinal lengthening (sham 29.9 cm; JC - 10.4 cm; p = 0.002).

CONCLUSION

Citrulline levels predict large differences in intestinal length and 'identify' SBS. However, citrulline cannot discriminate between adaptation in JI and JC, nor predict intestinal lengthening.

Serum Citrulline Levels Exhibit Circadian Variation and Fluctuations in Relation to Food Intake in Mice

Background

Plasma citrulline is a nonessential amino acid synthesized almost exclusively by enterocytes of the small intestine. Correlation between post-operative plasma citrulline levels and remnant small bowel mass and function has led to its use as a simple biomarker of functional intestinal mass in adults and children, with a proposed prognostic value for achieving enteral autonomy in the setting of intestinal failure. While it is standard to measure fasting levels in humans, the optimal timing of blood draws in relation to food intake and time of day has not been standardized and is poorly studied in animal models. We hypothesize that serum citrulline levels vary both throughout the day and with relation to food intake in mice.

Methods

Serum citrulline levels were measured from 12 C57BL/6 mice (6 - 9 weeks old) in the mornings and evenings, either after ad libitum food intake or after 8 - 12 h of access to water only. Blood draws for each experimental set-up were performed 1 week apart according to our Institutional Animal Care and Use Committee (IACUC) guidelines for acceptable blood collection volumes for survival procedures. At the end of the experiment, mice were euthanized and small intestine was harvested for morphometric measurements. Group means were compared using Student’s t-test with significance assumed for P < 0.05.

Results

After withholding chow for 8 - 12 h, serum citrulline levels were significantly greater in the morning compared to levels drawn in the evening. When mice were allowed ad libitum chow, there was no significant difference in serum citrulline levels drawn in the morning compared to the evening. There was no difference detected in villus height across the different experimental conditions.

Conclusions

Serum citrulline levels exhibit circadian variation and fluctuations in relation to food intake in mice, without apparent concurrent changes in enterocyte mass. There was no diurnal variation of serum citrulline levels in fed mice whereas fasted mice had significantly higher levels of serum citrulline in the morning compared to the evening. These findings underscore the paramount importance of consistent sample collection strategies in the setting of translational research.