Cancer cachexia induces host
protein wastage but the mechanisms are poorly understood.
Branched-chain amino acids play a regulatory role in the modulation of both
protein synthesis and degradation in host tissues.
Leucine, an important
amino acid in skeletal muscle, is higher oxidized in
tumor-bearing animals. A
leucine-supplemented diet was used to analyze the effects of Walker 256
tumor growth on body composition in young weanling Wistar rats divided into two main dietary groups: normal diet (N, 18%
protein) and
leucine-rich diet (L, 15%
protein plus 3%
leucine), which were further subdivided into control (N or L) or
tumor-bearing (W or LW) subgroups. After 12 days, the animals were sacrificed and their carcass analyzed. The
tumor-bearing groups showed a decrease in
body weight and fat content. Lean carcass mass was lower in the W and LW groups (W = 19.9 0.6, LW = 23.1 1.0 g vs N = 29.4 1.3, L = 28.1 1.9 g, P < 0.05).
Tumor weight was similar in both
tumor-bearing groups fed either diet. Western blot analysis showed that
myosin protein content in gastrocnemius muscle was reduced in
tumor-bearing animals (W = 0.234 0.033 vs LW = 0.598 0.036, N = 0.623 0.062, L = 0.697 0.065 arbitrary intensity, P < 0.05). Despite accelerated
tumor growth, LW animals exhibited a smaller reduction in lean carcass mass and muscle
myosin maintenance, suggesting that excess
leucine in the diet could counteract, at least in part, the high host
protein wasting in weanling
tumor-bearing rats.