C radiolabeling of proteins to monitor biodistribution of ingested proteins

• Published in: Analytical biochemistry Vol. 410; no. 1; pp. 57 - 61
• Main Authors: Davis, Laura D.R, Spencer, William J, Pham, Van Thong, Ward, Tonya L, Blais, David R, Mack, David R, Kaplan, Harvey, Altosaar, Illimar
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 01-03-2011
• Subjects: Animals; bovine serum albumin; carbon; Carbon Radioisotopes - analysis; Carbon Radioisotopes - chemistry; casein; Cattle; cost effectiveness; Eating; Freeze Drying; Humans; Isotope Labeling - methods; labels; lipopolysaccharides; methyl iodide; Methylation; Proteins - chemistry; Proteins - pharmacokinetics; radiolabeling; radionuclides; Rats; Rats, Sprague-Dawley; Solubility; stomach
• ISSN: 0003-2697; 1096-0309
• DOI: 10.1016/j.ab.2010.11.028

The economical preparation of microgram quantities of ¹⁴C-labeled proteins by in vacuo methylation with methyl iodide is described. The ¹⁴C radiolabeling was achieved by the covalent attachment of [¹⁴C]methyl groups onto amino and imidazole groups by reaction in vacuo with [¹⁴C]methyl iodide. The method was tested by investigating the biodistribution of ¹⁴C in rats that were fed ¹⁴C-labeled human soluble cluster of differentiation 14 (CD14) protein, a receptor for bacterial lipopolysaccharide. Two other control proteins, bovine serum albumin (BSA) and casein, were also labeled with ¹⁴C and used for comparative analysis to determine the following: (i) the efficacy and cost efficiency of the in vacuo radiolabeling procedure and (ii) the extent of incorporation of the ¹⁴C label into the organs of orogastrically fed 10-day-old Sprague–Dawley rats. [¹⁴C]BSA, [¹⁴C]casein, and [¹⁴C]CD14 were individually prepared with specific radioactivities of 34,400, 18,800, and 163,000 disintegrations per minute (dpm)/μg, respectively. It was found that the accumulation of ¹⁴C label in the organs of [¹⁴C]CD14-fed rats, most notably the persistence of ¹⁴C in the stomach 480min postgavage, was temporally and spatially distinct from [¹⁴C]BSA and [¹⁴C]casein-fed rats.