Thioredoxin treatment increases digestibility and lowers allergenicity of milk.
BACKGROUND
By resisting digestion in the stomach, the major bovine milk allergen, beta-lactoglobulin, is believed to act as a transporter of vitamin A and retinol to the intestines. beta-Lactoglobulin has 2 intramolecular disulfide bonds that may be responsible for its allergic effects.


OBJECTIVE
This study was carried out to assess the importance of disulfide bonds to the allergenicity and digestibility of beta-lactoglobulin.


METHODS
beta-Lactoglobulin was subjected to reduction by the ubiquitous protein thioredoxin, which was itself reduced by the reduced form of nicotinamide adenine dinucleotide phosphate by means of nicotinamide adenine dinucleotide phosphate-thioredoxin reductase. Digestibility was measured with a simulated gastric fluid; results were analyzed by SDS-PAGE. Allergenicity was assessed with an inbred colony of high IgE-producing dogs sensitized to milk.


RESULTS
As found for other proteins with intramolecular disulfide bonds, beta-lactoglobulin was reduced specifically by the thioredoxin system. After reduction of one or both of its disulfide bonds, beta-lactoglobulin became strikingly sensitive to pepsin and lost allergenicity as determined by skin test responses and gastrointestinal symptoms in the dog model.


CONCLUSIONS
The results provide new evidence that thioredoxin can be applied to enhance digestibility and lower allergenicity of food proteins.
del Val
G
G
Department of Plant and Microbial Biology, University of California, Berkeley, CA 94720, USA.
Yee
B C
BC
Lozano
R M
RM
Buchanan
B B
BB
Ermel
R W
RW
Lee
Y M
YM
Frick
O L
OL
D000818:Animals; D002417:Cattle; D004063:Digestion; D004064:Digestive System / Q000473:pathology; D004195:Disease Models, Animal; D004285:Dogs; D006801:Humans; D007782:Lactoglobulins / Q000737:chemistry / Q000276:immunology* / Q000378:metabolism*; D008892:Milk / Q000009:adverse effects / Q000276:immunology / Q000378:metabolism; D016269:Milk Hypersensitivity / Q000517:prevention & control*; D008958:Models, Molecular; D010084:Oxidation-Reduction; D010434:Pepsin A / Q000378:metabolism; D012882:Skin Tests; D013880:Thioredoxin-Disulfide Reductase / Q000378:metabolism; D013879:Thioredoxins / Q000378:metabolism*
D007782:Lactoglobulins; D013879:Thioredoxins; D013880:Thioredoxin-Disulfide Reductase; D010434:Pepsin A