Short Chain Fatty Acid Delivery: Assessing Exogenous Administration of the Microbiome Metabolite Acetate in Mice

Emerging studies have linked circulating short chain fatty acids (SCFAs), which are gut microbial fermentation byproducts, to positive effects on host physiology. Acetate (AC), the most abundant SCFA, enters the bloodstream via monocarboxylate transporters and diffusion. To study the in vivo effects of AC, various administration methods have been used in mice, but the effects of these methods on plasma AC are unknown. Thus, in this study we quantified changes in plasma AC over time after AC delivery in C57BL/6 mice using one of the three most commonly cited methods: drinking water (DW), intraperitoneal (IP) injection, or oral gavage (OG). Doses were chosen based on the literature. In all cases, the AC Colorimetric Assay Kit (Sigma) was used to detect AC concentration via changes in absorbance at 450nM. We validated this kit by demonstrating a concentration‐dependent increase in absorbance when a known concentration of acetate, but not other SCFAs or lactate (up to 1mM), were added to a sample. 4ul of plasma are required to measure a sample in triplicate. The absorbance mean of the baseline samples was set to one; all subsequent time points were averaged and normalized to one. For DW studies, mice (n=9) were treated with 200mM AC in DW for 21 days. Plasma samples were collected at 7 and 21 days of treatment, along with 7 days before and after treatment. There was no significant change in plasma AC during or following treatment. For IP studies, mice (n=9, 8) received an IP injection of AC at 0.5 or 1.0g/kg and plasma AC levels were measured at 0, 5, 15, 30, 45, 60, 120, and 180 mins. Both doses yielded a transient, sexdependent increase in plasma AC levels. At 0.5g/kg, AC levels were elevated above baseline at 5 and 15 mins in both sexes (p<0.0001) and in males at 30 mins (p<0.02). AC was higher in males than females at 15 mins (p<0.03). AC levels returned to baseline after 1 hr. In the 1g/kg cohort, plasma AC levels elevated above baseline at 5, 15, and 30 mins in both sexes (male p<0.0001, female p<0.02, <0.0001, and <0.05) and in males at 45 mins (p<0.001). Male AC levels were higher than female at 30 mins (p<0.03). AC levels returned to baseline by 3 hrs. Third, mice (n= 8, 8) received an OG of AC at either 1 or 2g/kg; plasma AC levels were measured at 0, 15, 30, 60, 90, 120, 180, and 300 mins. There were no significant sex differences between time points for either dose. For both doses, AC levels peaked at 15 mins (p <0.02). AC remained significantly elevated in the 1g/kg dose until 30 mins (p= 0.007) and in the 2g/kg dose at 60 and 90 mins (p< 0.05). In conclusion, AC delivery in DW at published doses does not elevate plasma AC, but AC is transiently elevated by IP and OG. Unchanged plasma AC by DW indicates that studies which have successfully altered physiology via DW delivery may be activating colonic, rather than systemic, signaling pathways. In addition, we find sex differences in the time course of plasma AC changes. In sum, these time course plasma measurements of AC can contribute to standardization in exogenous SCFA administration in mice, and aid in more precise interpretations of AC effects. Support or Funding Information NHLBI This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal .