Furthermore, despite the absence of differences in gross intestinal morphology between young and old mice, mean I-FABP protein levels, a protein considered as a marker of enterocyte damage but also having been shown to correlate with endotoxemia [54,55], in portal plasma were significantly higher in 24-month-old mice than in 4-month-old animals (Figure 2J). Here, FABP2 is linked to serum lipopolysaccharide activity.