Increased availability of leucine with leucine-rich whey proteins improves postprandial muscle protein synthesis in aging rats.
OBJECTIVE
We previously found that aging was characterized by a decreased sensitivity of muscle protein synthesis to leucine and that a free leucine-supplemented diet corrected this defect in old rats and elderly humans. The present experiment was undertaken to evaluate the efficiency of selected leucine-rich proteins to stimulate postprandial muscle protein synthesis in old rats to optimize nutritional protein support in the elderly.


METHODS
Sixty rats (22 mo old) received an experimental meal for the first hour of feeding and a standard diet for the rest of the day for 30 d. Experimental meals contained milk proteins that differed in leucine content: beta-lactoglobulin (14.5% leucine), Prolacta (13.4%), alpha-lactalbumin (10.9%), and casein (10%). As a control, a fifth group was added that received herring flour protein (7.3% leucine). Muscle protein synthesis was determined in vivo in the postprandial state at the end of the 30-d nutritional period using the flooding dose method (1-(13)C phenylalanine).


RESULTS
Leucine intake and plasma leucine concentrations were significantly increased in rats fed meals containing the leucine-rich proteins (i.e., beta-lactoglobulin and Prolacta). As previously observed with free leucine-supplemented meals, postprandial muscle protein synthesis was significantly improved in rats fed the meals containing the leucine-rich proteins. Interestingly, the beneficial effect was maintained after the 30-d supplementation.


CONCLUSIONS
The results indicated that leucine-rich proteins were efficient in improving muscle protein synthesis in old rats. Thus, nutritional supplements containing such proteins may be efficient in preventing sarcopenia in the elderly and would represent a safe and optimized nutritional strategy. However, further experiments are necessary to determine the duration of such nutritional support to obtain a significant protein gain in muscle.
Rieu
Isabelle
I
Unité de Nutrition Humaine, UMR 1019, Institut National de la Recherche Agronomique-Centre de Recherche en Nutrition Humaine d'Auvergne, Saint Genès Champanelle, France.
Balage
Michèle
M
Sornet
Claire
C
Debras
Elisabeth
E
Ripes
Sandrine
S
Rochon-Bonhomme
Cécile
C
Pouyet
Corinne
C
Grizard
Jean
J
Dardevet
Dominique
D
D000375:Aging / Q000097:blood / Q000502:physiology*; D000596:Amino Acids / Q000097:blood; D000818:Animals; D002247:Carbon Isotopes; D004305:Dose-Response Relationship, Drug; D007930:Leucine / Q000097:blood / Q000378:metabolism / Q000493:pharmacokinetics*; D008297:Male; D008894:Milk Proteins; D009124:Muscle Proteins / Q000096:biosynthesis*; D019518:Postprandial Period; D011897:Random Allocation; D051381:Rats; D017208:Rats, Wistar; D000067816:Whey Proteins
D000596:Amino Acids; D002247:Carbon Isotopes; D008894:Milk Proteins; D009124:Muscle Proteins; D000067816:Whey Proteins; D007930:Leucine