Figure 1. Microbial-Derived Short-Chain Fatty Acids Promote Localized O₂ Depletion.

(A) Mice (n = 12) were administered PMDZ 30 min prior to sacrifice. Colon samples were paraffin-embedded and stained according to the manufacturer’s instructions and counterstained with DAPI.

(B) For analysis of “physiologic hypoxia” along the length of the lumen-to-serosa axis, samples (n = 3 per animal) were photographed and imported into ImageJ, where 100 μm sections were divided into equivalent 10 μm and quantified for PMDZ retention. Results are pooled and plotted as fluorescence intensity per μm².

(C–E) Real-time O₂ content in responses to 10 mM NaB (C), acetate (D), and propionate (E) (blue) were compared to vehicle control (black). Inhibition of oxidative phosphorylation by the addition of oligomycin to each SCFA treatment increased O₂ content in media (red). Error bars represent SEM.

(F and G) The rate of O₂ consumption 30 min after treatment with NaB (F) and acetate (G) was increased (p < 0.05).

(H) Sodium propionate did not significantly influence the rate of O₂ consumption.

(I) O₂ content of media was inversely related to concentration of NaB treatment with the greatest decrease at the physiologic concentration of 10 mM (p < 0.01).

(J) Rate of O₂ consumption 30 min after treatment was also greatest with 10 mM NaB (p < 0.01).

(K) Validation of the method for O₂ consumption using the XF Analyzer. Shown here is the influence of buffer (closed circles) and 10mM NaB (closed squares) on Caco2 cell O₂ consumption over a period of 100 min (p < 0.01).

(L and M) Mitochondria-depleted Caco2 cells (L) consumed less O₂ compared with control after exposure to NaB (M). Data represent mean ± SEM from three ([I]–[M]) or four ([A]–[H]) independent experiments. Significance was determined using one-way ANOVA ([F]–[K]) and Student’s t test ([L] and [M]).