Determination of the rat tissue partitioning of endotoxin in vitro for physiologically-based pharmacokinetic (PBPK) modeling

The biosynthetically double‐labeled lipopolysaccharide (LPS), containing 3H‐labeled on the fatty acyl‐chains and 14C‐labeled on the glucosamine of Salmonella enterica serotype typhimurium, was isolated from bacteria grown in proteose peptone‐beef extract (PPBE) medium in the presence of labeled precursors; 133 µCi/ml of [2‐3H] acetate sodium salt and 0.167 µCi/ml of N‐acetyl[D‐1‐14C]glucosamine. The LPS was extracted from the bacteria with 90% phenol/chloroform/petroleum ether, purified and stored in 0.1% (v/v) triethylamine/10 mM Tris HCl at −70 °C. Tissue slices and portions of the meninges were prepared and incubated in artificial cerebrospinal fluid (CSF) or Krebs phosphate buffer (Krebs) containing 150 ng/ml LPS with [3H] LPS (0.004 µCi/ml, sp. act. 28 µCi/mg LPS). The tissues were incubated under 95% oxygen/5% carbon dioxide at 37 °C with constant agitation until steady‐state uptake was reached (60 min). At the end of the incubation period, tissues were processed for radioactivity measurement. The rat tissue partitioning of LPS in artificial CSF for brain and Krebs for other organs was measured by using the ratio of tissue to medium at the steady state in vitro. The following results were obtained from the study: Heart, 0.15; liver, 0.19; spleen, 0.12; kidney, 0.18; stomach, 0.17; small intestine, 0.18; brain stem, 0.10; cerebellum, 0.11; meninges, 0.77; hippocampus, 0.12; hypothalamus, 0.12; frontal cortex, 0.09 and caudate nucleus, 0.10. This information, along with plasma or blood/buffer partition coefficients, is a requisite for constructing a physiologically‐based pharmacokinetic (PBPK) model of endotoxins for quantitative risk assessment. Copyright © 2004 John Wiley & Sons, Ltd.