Short-chain fatty acid delivery: assessing exogenous administration of the microbiome metabolite acetate in mice.

Short-chain fatty acids (SCFAs) are fermentation by-products of gut microbes which have been linked to positive effects on host physiology; the most abundant SCFA is acetate. Exogenous administration of acetate alters host metabolism, immune function, and blood pressure, making it a biologic of interest. The effects of acetate have been attributed to activation of G-protein-coupled receptors and other proteins (i.e., HDACs), often occurring at locations distant from the gut such as the pancreas or the kidney. However, due to technical difficulties and costs, studies have often delivered exogenous acetate without determining if systemic plasma acetate levels are altered. Thus, it is unclear to what extent each method of acetate delivery may alter systemic plasma acetate levels. In this study, we aimed to determine if acetate is elevated after exogenous administration by drinking water (DW), oral gavage (OG), or intraperitoneal (IP) injection, and if so, over what timecourse, to best inform future studies. Using a commercially available kit, we demonstrated that sodium acetate delivered over 21 days in DW does not elicit a measurable change in systemic acetate over baseline. However, when acetate is delivered by OG or IP injection, there are rapid, reproducible, and dose-dependent changes in plasma acetate. These studies report, for the first time, the timecourse of changes in plasma acetate following acetate administration by three common methods, and thus inform the best practices for exogenous acetate delivery.

Sodium reduction during cardiopulmonary bypass: Plasma-Lyte 148 versus trial fluid as pump primes.

OBJECTIVES: We compared effects on plasma sodium concentrations plus calculated plasma tonicity of two "balanced" crystalloid solutions used as 2 L pump primes during cardiopulmonary bypass (CPB): Plasma-Lyte 148 (sodium concentration, 140 mmol/L; potassium concentration, 5 mmol/L) versus a bicarbonate-balanced fluid (sodium concentration, 140 mmol/L; potassium concentration, 0 mmol/L). DESIGN, SETTING AND PARTICIPANTS: We analysed pooled data from two prospective interventional studies performed in university-affiliated hospitals, from 50 patients undergoing elective cardiac surgery. INTERVENTIONS: Participants were allocated equally to Plasma-Lyte 148 or bicarbonate-balanced fluid, with plasma electrolytes measured by direct ion selective electrodes immediately before bypass (pre-CPB), within 3 minutes of commencement (T2), and before bypass cessation (end-CPB). RESULTS: Plasma sodium fell at T2 in 46 patients (92%) (P<0.0005). With Plasma-Lyte 148, the mean sodium decreased by 3.0 mmol/L (SD, 1.7 mmol/L), and with bicarbonate-balanced fluid it decreased by 2.2 mmol/L (SD, 1.1 mmol/L) (P=0.002). The mean tonicity fell by >5 mOsm/kg for both groups (P<0.0005). At end-CPB, the mean sodium for both groups remained reduced by >2 mmol/L (P<0.0005). In the group receiving Plasma-Lyte 148, 52% of patients were hyponatraemic (sodium<135 mmol/L) at T2 and end-CPB. CONCLUSIONS: Sodium reductions were common with both priming solutions, but more severe with Plasma-Lyte 148. Crystalloid priming solutions require sodium concentrations>140mmol/L to ensure normonatraemia throughout CPB.

Isotopomics: a top-down systems biology approach for understanding dynamic metabolism in rats using [1,2-(13)C(2)] acetate.

Isotope labeled tracers are commonly used to quantify the turnover rates of various metabolic intermediates and yield information regarding physiological regulation. Studies often only consider either one nutritional state (fasted or fed) and/or one question (e.g., measure of lipid or protein turnover). In this article, we consider a novel application combining the global approach of metabonomics with widespread stable isotope labeling as a way of being able to map metabolism in open mammalian systems, an approach we call "isotopomics". A total of 45 15-week-old male Zucker rats were administrated different amounts (from 0.5 to 8 mmol/kg) of sodium [1,2-(13)C(2)] acetate. Plasma samples taken at 1, 4, and 24 h were analyzed with (13)C nuclear magnetic resonance (NMR) and gas chromatography/mass spectrometry (GC/MS) to measure (13)C isotopic enrichment of 39 plasma metabolites across a wide range of compound classes (amino acids, short-chain fatty acids, lactate, glucose, and free fatty acids). Isotopic enrichment from 0.1-7.1 mole percent excess (MPE) for the highest dose could be reliably measured in 16 metabolites, and the kinetics of their (13)C isotopic enrichment are reported. Clustering metabolites based on (13)C kinetic curves enabled highlighting of time dependent patterns of (13)C distribution through the key metabolic pathways. These kinetic and quantitative data were reported into a biochemical map. This type of isotopomic approach for mapping dynamic metabolism in an open system has great potential for advancing our mechanistic knowledge of how different interventions and diseases can impact the metabolic response of animals and humans.

Michaelis-Menten elimination kinetics of acetate in rabbit.

BACKGROUND: Acetate redistribution from hepatic to peripheral tissues was reported during ethanol metabolism when saturating conditions were reached for acetate metabolism. Because this redistribution cannot be clarified by linear kinetics, elimination kinetics of acetate was studied in the rabbit. METHODS: A sodium-acetate solution in physiological saline (0.5 and 1.0 g/kg of body weight) was injected as an intravenous bolus. The blood acetate profile was measured by headspace gas chromatography. RESULTS: Blood acetate disappeared rapidly. Statistical moment analysis of the blood acetate profiles showed that the normalized area under the curve and the mean residence time increased with an increasing dose amount. These increases suggested a capacity-limited elimination of acetate. Simultaneous multilines fitting after two acetate doses was used to estimate the pharmacokinetic model by the application of minimum Akaike's information criterion estimation. As a result, the blood acetate concentration-time curve was best described by a two-compartment open model with Michaelis-Menten elimination kinetics. The Vmax value was approximately two times larger than that of ethanol obtained by using the same compartment model. The Km value (1.5 mM) was almost the same as that of ethanol and corresponded to blood acetate levels during ethanol oxidation that had been reported to be approximately 2 mM. CONCLUSION: The elimination of acetate obeys nonlinear kinetics, which can clarify the saturation of acetate metabolism.

Quantitative bioanalysis utilizing high-performance liquid chromatography/electrospray mass spectrometry via selected-ion monitoring of the sodium ion adduct [M+Na]+.

A high-performance liquid chromatography (HPLC)/electrospray mass spectrometric method for quantitative determination of a compound in dog plasma was developed and validated via the selected-ion monitoring of the electrospray-generated [M+Na]+ adduct of the compound. The plasma samples were acidified with HCl and then extracted with methyl tert-butyl ether. The reconstituted extracts were injected into an HPLC/positive-ion electrospray ionization mass spectrometry system. The HPLC mobile phase consisted of acetonitrile, water, formic acid (3 mM) and sodium acetate (0.3 mM). This composition of mobile phase provided the optimum electrospray condition for the formation of the [M+Na](+)-ion. This work demonstrates that the addition of sodium acetate into the HPLC mobile phase and the subsequent selected-ion monitoring of the sodium ion adduct of the analyte is a viable approach in quantitative bioanalysis. The facile formation of the sodium ion adduct of the analyte, which does not contain functional groups that are known to be strong proton acceptors, appears to be a function of the particular electrospray instrument used.