Hepatic uptake and metabolism of benzoate: a multiple indicator dilution, perfused rat liver study

Abstract

Multiple, noneliminated references ((51)Cr-labeled erythrocytes, (125)I-albumin, [(14)C]- or [(3)H]sucrose, and [(2)H](2)O), together with [(3)H]hippurate or [(14)C]benzoate, were injected simultaneously into the portal vein of the perfused rat liver during single-pass delivery of benzoate (5-1,000 microM) and hippurate (5 microM) to investigate hippurate formation kinetics and transport. The outflow dilution data best fit a space-distributed model comprising vascular and cellular pools for benzoate and hippurate; there was further need to segregate the cellular pool of benzoate into shallow (cytosolic) and deep (mitochondrial) pools. Fitted values of the membrane permeability-surface area products for sinusoidal entry of unbound benzoate were fast and concentration independent (0.89 +/- 0.17 ml. s(-1). g(-1)) and greatly exceeded the plasma flow rate (0.0169 +/- 0.0018 ml. s(-1). g(-1)), whereas both the influx of benzoate into the deep pool and the formation of hippurate occurring therein appeared to be saturable. Results of the fit to the dilution data suggest rapid uptake of benzoate, with glycination occurring within the deep and not the shallow pool as the rate-determining step.

Modulatory Effects of Gut Microbiota on the Central Nervous System: How Gut Could Play a Role in Neuropsychiatric Health and Diseases

“…137,138 Hippurate is an end-product of the metabolism of dietary proteins and phenolic acids, and is formed by the liver from benzoic acid. 139 Benzoic acid is a product of protein metabolism by gut microbiota, and altered hippurate level points towards altered metabolism in protein, potentially caused by altered gut microbiota. 140 Another study has reported significant difference in children with autism and normal children in the fatty acid composition of phospholipids, with autistic children having an increased level of most of the saturated fatty acids, except for propionic acid, and a decreased level of polyunsaturated fatty acids.…”

Moment Analysis of Metabolic Heterogeneity: Conjugation of Benzoate with Glycine in Rat Liver Studied by Multiple Indicator Dilution Technique

“…Cell suspensions of PP or PV hepatocytes, preincubated at 37°C for 10 min, were added to mixtures of [ 14 C]benzoate and unlabeled benzoate to result in concentrations of 480,000 Ϯ 136,000 dpm/ml and 1 M in 1.6 to 1.7 ϫ 10 6 cells/ml. Duplicate samples (100 l) were retrieved simultaneously at various times (0.5-7.5 min) directly into a 1.5-ml microcentrifuge tube containing 0.5 ml of acetonitrile (and internal standard, methoxybenzoic acid) for HPLC analysis using a reversephase Beckman Ultrasphere column as previously described (Chiba et al, 1994;Cong et al, 2001;Schwab et al, 2001). The samples were mixed well and stored at Ϫ20°C until analysis.…”

“…Perfusate was gassed simultaneously with 95% oxygen/5% carbon dioxide (Matheson, Mississauga, ON) and oxygen (BOC Gases, Whitby, ON, Canada), and the pH, monitored by an "on-line" flow-through pH electrode (Thermo Orion, Boston, MA), was maintained at 7.4 by adjusting the proportion of the two gas supplies. Three to five inflow and outflow perfusate samples, collected during steady state, were used for determination of the average input (C In ) and output (C Out ) perfusate concentrations of unlabeled benzoate and hippurate; both benzoate and hippurate do not distribute into red blood cells (Yoshimura et al, 1998;Schwab et al, 2001). Bile samples were collected for the first 15 min and at 5-to 10-min intervals thereafter up to 60 min to monitor the excreted radioactivity and the bile flow; the total recovery relative to the injected dose was found to be minimal.…”

“…Transport is likely attributed to the monocarboxylic acid transporter 1 (Tamai et al, 1999) that transports L-lactate and is evenly distributed in the acinus (Staricoff et al, 1995). Although the mitochondria space for metabolism constitutes an added, intracellular compartment (Chiba et al, 1994;Schwab et al, 2001) (Goresky et al, 1973) and were compared with those observed previously for prograde flow under first-order conditions (Ͻ200 M benzoate) (Schwab et al, 2001). However, due to our inability to encompass heterogeneity into the Goresky model, the previously developed tubes-in-series model (Schwab and Pang, 1999) was extended to encompass heterogeneity in mitochondrial metabolism behind transport barriers.…”

“…The metabolite, hippurate, undergoes saturable, barrier-limited transport into the rat liver, and is neither metabolized nor excreted into bile (Yoshimura et al, 1998). Benzoate also undergoes barrier-limited transport but is transported linearly and rapidly into hepatocytes at concentrations below 1 mM (Schwab et al, 2001). Transport is likely attributed to the monocarboxylic acid transporter 1 (Tamai et al, 1999) that transports L-lactate and is evenly distributed in the acinus (Staricoff et al, 1995).…”