Noninvasive Monitoring of Small Intestinal Oxygen in a Rat Model of Chronic Mesenteric Ischemia

Abstract

We noninvasively monitored the partial pressure of oxygen (pO2) in rat small intestine using a model of chronic mesenteric ischemia by electron paramagnetic resonance oximetry (EPR) over a 7-day period. The particulate probe lithium octa-n-butoxynaphthalocyanine (LiNc-BuO) was embedded into the oxygen permeable material polydimethyl siloxane (PDMS) by cast-molding and polymerization (Oxy-Chip). A one-time surgical procedure was performed to place the Oxy-Chip on the outer wall of the small intestine (SI). The superior mesenteric artery (SMA) was banded to approximately 30% blood flow for experimental rats. Noninvasive measurement of pO2 was performed at baseline for control rats or immediate post-banding and on days 1, 3, and 7. The SI pO2 for control rats remained stable over the 7-day period. The pO2 on day 7 was 54.5 ± 0.9 mmHg (mean ± SE). SMA banded rats were significantly different from controls with a noted reduction in pO2 post banding with a progressive decline to a final pO2 of 20.9 ± 4.5 mmHg (mean ± SE; p = 0.02). All SMA-banded rats developed adhesions around the Oxy-Chip yet remained asymptomatic. The hypoxia marker Hypoxyprobe™ was used to validate low tissue pO2. Brown cytoplasmic staining was consistent with hypoxia. Mild brown staining was noted predominantly on the villus tips in control animals. SMA-banded rats had an extended region of hypoxic involvement in the villus with a higher intensity of cytoplasmic staining. Deep brown staining of the enteric nervous system neurons and connective tissue both within layers and in the mesentery were noted. SMA banded rats with lower pO2 values had a higher intensity of staining. Thus, monitoring SI pO2 using the probe Oxy-Chip provides a valid measure of tissue oxygenation. Tracking pO2 in conditions that produce chronic mesenteric ischemia will contribute to our understanding of intestinal tissue oxygenation and how changes impact symptom evolution and the trajectory of chronic disease.

Redox signaling mediated by the gut microbiota

“…A non-invasive method of determining tissue pO 2 by electron paramagnetic resonance (EPR) oximetry showed oxygen levels of less than 2% in the intestinal lumen, 8% in the small intestinal wall, and 3 % at the villus tip [105]. These conditions of physiological oxygenation were termed physioxia.…”

A novel human enteroid-anaerobe co-culture system to study microbial-host interaction under physiological hypoxia

“…It has been shown that the pericellular oxygen concentration of Caco-2 cells cultured in ambient incubator conditions (18-21% oxygen) can drop to 16% oxygen when cells are cultured on membrane inserts 18 . This high level of oxygenation observed under standard incubator conditions serves as a significant confounding factor when considering that in vivo oxygen levels range from 1%-11% oxygen 13,19 . Additionally, altered gene-expression and phenotypes have been observed when comparing aerobic cultures to cultures grown at physiologic levels of oxygen, suggesting that ambient oxygen induces hyperoxic, potentially atypical, phenotypes in cell culture 20 .…”

Good, Bad, or Risky? : intestinal permeability to protein: human and in vitro studies

“…Gardner [40,41] already discussed upon this topic, but there is still limited evidence that larger peptides and protein are taken up intactly by the intestine [42,43]. From the existence of food allergies, however, it can be deduced that indeed a small amount of immunologically active food protein can be taken up and enter the circulation [44]. In this thesis, I will examine whether this also applies for several specifically chosen dietary proteins and peptides and whether a physiological challenge, in this case exercise, can affect this uptake.…”

“…Two important AAs in citrulline metabolism are glutamine and arginine, as a precursor and product of citrulline, respectively. Depletion of glutamine, which is the main fuel for enterocytes, results in plasma citrulline depletion [44,45]. Findings in mice suggest that during shortage of available glutamine, enterocytes possibly prioritize its utilization for energy over the production of citrulline [46].…”

“…A lower supply of oxygen affects especially the intestine, as this organ is particularly sensitive to changes in oxygen supply. This is because the intestinal epithelium exists in a state of relative 'physiological hypoxia', already under normal physiological conditions [42][43][44]. Therefore small changes in oxygen supply can already lead to oxygen deprivation, which in turn can result in mitochondrial ATP depletion.…”