title: Assessment of the inhibition of ricin toxicity by lactose in milk.
abstract: The effect of lactose at the concentration typically found in milk (134 mM) on the ability of ricin to inhibit protein synthesis in HeLa cells was studied. Ricin (0.001 to 300 μg/ml) that was either not treated or treated with 134 mM lactose was added to test tubes containing 1 ml of HeLa cells (approximately 3 × 10(5) cells in a low-leucine medium). After 2 h of incubation at 37°C, 0.5 μCi of L-[U-(14)C]-leucine was added to each tube and incubated for another 60 min. The cells were harvested by centrifugation and lysed, and cellular proteins were separated. The amount of radioactivity incorporated into the proteins was determined by liquid scintillation. The biological activity of ricin, i. e., the amount of radioactivity in a sample relative to that of the control (cells not treated with ricin), was calculated for each treatment. The inhibitory effect of 134 mM lactose on the biological activity of ricin was only significant at concentrations of ricin below 1 μg/ml. At higher ricin concentrations, the effect of 134 mM lactose decreased as the concentration of ricin increased, resulting in an increase in the inhibition of proteins synthesis. Our results also indicated that bovine milk, when used in place of 134 mM lactose, was more effective for reducing the activity of ricin at concentrations below 1 μg/ml but was ineffective against ricin concentrations greater than 1 μg/ml. These results suggest that milk may not protect against ricin intoxication at the concentration (0.89 μg/ml) equivalent to the lowest limit of its 50 % lethal dose for a 20-kg child consuming 225 ml (8 oz) of milk.
authors.affiliation: Department of Food Science and Nutrition, University of Minnesota, 1334 Eckles Avenue, Saint Paul, Minnesota 55108, USA; Department of Human Ecology, Delaware State University, 1200 North DuPont Highway, Dover, Delaware 19901, USA.
authors.forename: Stephen E
authors.initials: SE
authors.lastname: Lumor
authors.forename: Bronwyn D
authors.initials: BD
authors.lastname: Deen
authors.forename: Ian
authors.initials: I
authors.lastname: Ronningen
authors.forename: Kenneth
authors.initials: K
authors.lastname: Smith
authors.forename: Neal R
authors.initials: NR
authors.lastname: Fredrickson
authors.forename: Francisco
authors.initials: F
authors.lastname: Diez-Gonzalez
authors.forename: Theodore P
authors.initials: TP
authors.lastname: Labuza
mesh_terms: D000818:Animals; D002417:Cattle; D004305:Dose-Response Relationship, Drug; D005506:Food Contamination / Q000032:analysis*; D006367:HeLa Cells; D006801:Humans; D007785:Lactose / Q000494:pharmacology*; D008892:Milk / Q000201:enzymology* / Q000378:metabolism; D014176:Protein Biosynthesis / Q000187:drug effects; D012276:Ricin / Q000037:antagonists & inhibitors* / Q000378:metabolism
chemical_list: D012276:Ricin; D007785:Lactose