Radiolabeled cholesteryl ethers: A need to analyze for biological stability before use

Abstract

Radiolabeled cholesteryl ethers are widely used as non-metabolizable tracers for lipoproteins and lipid emulsions in a variety of in vitro and in vivo experiments. Since cholesteryl ethers do not leave cells after uptake and are not hydrolyzed by mammalian cellular enzymes, these compounds can act as markers for cumulative cell uptakes of labeled particles. We have employed [3H]cholesteryl oleoyl ether to study the uptake and distribution of triglyceride-rich emulsion particles on animal models. However, questionable unexpected results compelled us to analyze the stability of these ethers. We tested the stability of two commercially available radiolabeled cholesteryl ethers - [3H]cholesteryl oleoyl ether and [3H]cholesteryl hexadecyl ether from different suppliers, employing in vitro, in vivo and chemical model systems. Our results show that, among the two cholesteryl ethers tested, one ether was hydrolyzed to free cholesterol in vitro, in vivo and chemically under alkaline hydrolyzing agent. Free cholesterol, unlike cholesteryl ether, can then re-enter the circulation leading to confounding results. The other ether was not hydrolyzed to free cholesterol and remained as a stable ether. Hence, radiolabeled cholesteryl ethers should be analyzed for biological stability before utilizing them for in vitro or in vivo experiments.

In vivo monitoring of hepatic glycolipid distribution of <i>n</i>-6 ∕ <i>n</i>-3 in jugular-vein-cannulated rats as a nutritional research model for monogastric animal

“…In such a case, when lipid metabolism in the body progresses, the liver incorporation rate of 3 H-labeled material shows a much higher value than that of 14 C-labeled material. However, the 3 H incorporation rate into the blood is so much lower or almost zero (Wilfling et al, 2013;Grevengoed et al, 2014;Park, 2016;Kollareth et al, 2018). Unlike cholesteryl [ 14 C] oleate, [ 3 H]-cholesteryl oleoyl ether does not go through a metabolism path like the liver.…”

Acute injection of a DHA triglyceride emulsion after hypoxic-ischemic brain injury in mice increases both DHA and EPA levels in blood and brain✰

“…The tri-DHA treatment regimen, proven effective and safe, was based on previous studies from our laboratory [22,23]. Total lipids were extracted as described previously [34]. Plasma PL, NEFA, TG and cholesteryl esters (CE) were separated by thin layer chromatography (TLC) using the solvent system hexane:diethyl ether:acetic acid (70:30:1) [34].…”

“…Total lipids were extracted as described previously [34]. Plasma PL, NEFA, TG and cholesteryl esters (CE) were separated by thin layer chromatography (TLC) using the solvent system hexane:diethyl ether:acetic acid (70:30:1) [34]. Plasma LPC were separated by onedimensional TLC employing the solvent system chloroform:methanol:acetic acid:acetone:water (40:25:7:4:2) [35].…”

Acute Injection of Omega-3 Triglyceride Emulsion Provides Very Similar Protection as Hypothermia in a Neonatal Mouse Model of Hypoxic-Ischemic Brain Injury

“…Tissues and organs were homogenized using a Polytron Tissue Disruptor (Omni TH, Kenneswa, GA) and the radioactivity measured by liquid scintillation spectrometry ( 29 ). The samples were suspended in scintillation fluid (Ultima Gold scintillation fluid, PerkinElmer, Boston, MA), mixed and 3 H dpm assayed in a PerkinElmer Tri-Carb liquid scintillation spectrometer 5110 TR.…”