Fluorescence imaging in vivo visualizes delayed gastric emptying of liquid enteral nutrition containing pectin

Abstract

Background: Semi-solidification by gelation or increased viscosity could slow the influx of liquid enteral nutrition (EN) into the small intestine. A liquid EN formula containing pectin that gels under acidic conditions such as those found in the stomach has been developed. A new near-infrared fluorescent imaging reagent was used to non-invasively acquire real time images of gastric emptying in a murine model in vivo. We postulated that the EN formula delays gastric emptying and tested this hypothesis using imaging in vivo.

Methods: Male BALB/c mice were given an oral bolus injection of a liquid EN containing the fluorescence reagent GastroSense750 with or without pectin. The EN in the stomach was visualized in vivo at various intervals using a non-invasive live imaging system and fluorescent signals were monitored from the stomach, which was removed at 60 min after EN ingestion.

Results: The fluorescence intensity of signals in stomachs in vivo and in resected stomachs was lower and attenuated over time in mice given EN without, than with pectin.

Conclusions: Adding a gelling agent such as pectin delayed the transit of liquid EN from the stomach. Fluorescence imaging can visualize the delayed gastric emptying of EN containing pectin.

Figure 1

Viscosity of enteral nutrition mixed with artificial gastric juice and schema of experimental design. A. Effect of shear rate on viscosity measurements of EN with (filled circles) and without (unfilled circles) pectin mixed with equal amount of artificial gastric juice. B. Schema of experimental design. Mice fasted for 24 hrs were injected with 10 μL/g body weight of enteral nutrition (0 min; ▲) 2 h after withdrawing drinking water (■). Gastric imaging proceeded 5, 15, 30, 45, 60 minutes after injection under isoflurane anesthesia (●). Isolated stomachs were assessed thereafter (◇).

Figure 2

Representative ventral images of fluorescence emission of gastric contents. Mice received a bolus of 10 μL/g body weight of liquid EN (Hine® E-gel) containing 1.25 pmol of GastroSense™750 fluorescence imaging agent without (A) or with (B) pectin. Representative ventral images of anesthetized mice are shown at baseline and at 5, 15, 30, 45, and 60 min later to monitor gastric EN. All images were acquired using the same pseudocolor scale of radiance to show relative changes in bioluminescence emission over time.

Figure 3

Gastric residue of enteral nutrition in mice. Gastric fluorescence is represented on Y-axis as measure of gastric residue of enteral nutrition. Values from mice weighing 22–25 g (n = 8 per group) without (unfilled circles) and with (filled circles) pectin over time are shown as means ± SD. *p < 0.05 (Student’s t test).

Figure 4

Fluorescence emission in enteral nutrition residues from resected stomachs of mice at 60 min after ingestion. A. Representative images of fluorescence values derived from gastric contents of mice that were given liquid EN bolus containing fluorescent imaging agent without (a) or with (b) pectin. Fluorescence emission on Y-axis as indicates gastric residues of enteral nutrition. Values from mice (n = 8 per group) without (unfilled bars) and with (filled bars) pectin are shown as means ± SD. *p < 0.05 (Student’s t test). B. Regression analysis of fluorescence emitted by enteral nutrition residues with (filled circles) and without (unfilled circles) pectin in resected stomachs vs. stomachs imaged at 60 min after ingestion in vivo.