Discussion
chronic exercise-induced gastrointestinal, endotoxemia, GI distress, acute GI stress, inflammatory bowel diseases, GI injury, intestinal injury
INFLAMMATORY BOWEL DISEASES, ENDOTOXEMIA
The main finding of this study is that supplementation with CP (10 g/day for 8 days) before high intensity running exercise did not alter markers of GI integrity as measured by our primary outcome I-FABP. Collagen peptides also had no effect on GI permeability (L/R). However, at 2-h post-exercise, serum LPS remained low after CP supplementation (+ 14.6 pg/ml vs. REST) but significantly increased after the CON trial (+ 71.8 pg/ml), suggesting CP may have attenuated systemic increases in exercise-induced LPS.Neither I-FABP or L/R were modulated by CP using this model of exercise-induced GI distress. As this was the first study to examine the effects of CP on permeability and GI injury in humans, direct comparisons to previous research are not possible. While there is in vitro research in Caco-2 cells showing that CP reduces NF-κB mRNA, and increases the expression of tight junction proteins that protect the intestinal barrier from insults [Serum LPS concentrations, a measure of endotoxemia, were elevated above pre-exercise levels in the CP and CON trials at 2 h post. This is in line with some [Although circulatory increases in LPS are often attributed to epithelial damage and paracellular transport through the intestinal barrier, the exact mechanisms by which LPS reaches the circulation are unclear [There were no major differences in GI symptoms between the CP and CON trials. However, given that subjective GI symptoms do not always correlate with injury and permeability markers, other non-GI factors may be involved [There are some limitations that should be acknowledged. We only standardized dietary intake in the 24 h prior to main trials and therefore cannot rule out that differences in habitual dietary intake in the days prior to this impacted the findings. In addition, while the high intensity exercise bout increased I-FABP concentrations, indicative of epithelial intestinal injury, there was no statistically significant increase in permeability after exercise, as measured by L/R—albeit there was a medium effect size for increases in lactulose compared to the REST trial. A non-statistically significant increase in L/R is not uncommon, with two similar studies in which subjects ran for 60 min at 70% A strength of the study is that heart rate, RPE, thermal comfort, plasma volume changes, and core temperature were not significantly different in the CON and CP trials, indicating the exercise trials were well matched for intensity, and therefore any between trials changes are unlikely due to variations in the exercise protocols. In addition, this is the first in vivo human study to examine CP in this context and provides a rationale for future studies. Future research is warranted with longer dosing strategies, higher doses of CP, different timings of intake, other acute GI stress models, and/or in volunteers with marked GI symptoms or chronic exercise-induced gastrointestinal conditions. Future studies should also include additional markers associated with GI distress and inflammatory bowel diseases such as ZO-1, alpha-1-antitrypsin and calprotectin.