Use of an intravenous branched chain amino acid enriched diet in the tumor-bearing rat

Metabolic Remodeling in Skeletal Muscle Atrophy as a Therapeutic Target

Skeletal muscle is a highly responsive tissue, able to remodel its size and metabolism in response to external demand. Muscle fibers can vary from fast glycolytic to slow oxidative, and their frequency in a specific muscle is tightly regulated by fiber maturation, innervation, or external causes. Atrophic conditions, including aging, amyotrophic lateral sclerosis, and cancer-induced cachexia, differ in the causative factors and molecular signaling leading to muscle wasting; nevertheless, all of these conditions are characterized by metabolic remodeling, which contributes to the pathological progression of muscle atrophy. Here, we discuss how changes in muscle metabolism can be used as a therapeutic target and review the evidence in support of nutritional interventions and/or physical exercise as tools for counteracting muscle wasting in atrophic conditions.

An overview of amines as nutritional supplements to counteract cancer cachexia

Cancer cachexia is a complex multifactorial syndrome characterized by loss of skeletal muscle mass (with or without loss of fat mass) that cannot be fully reversed by conventional nutritional support and leads to progressive functional impairment. Recently, some amino acids and other amine dietary supplements have been highlighted in medical field due to positive effects upon diseases evolving skeletal muscle atrophy. Therefore, the aim of this brief review is to discuss the putative application of amines as dietary supplements to counteract skeletal muscle wasting on cancer cachexia. Specifically, we focus in two nutritional supplements: (1) branched-chain amino acids (BCAAs) and (2) creatine. Both BCAAs and creatine may attenuate proteolysis and enhance proteins synthesis in skeletal muscle. Although more experimental studies and clinical trials are still necessary to elucidate this therapeutic application, several evidences have demonstrated that amines supplementation is a promising coadjuvant treatment to cancer cachexia.

Investigations of branched-chain amino acids and their metabolites in animal models of cancer

Many of the features of BCAA metabolism in the tumor-bearing state are similar to the other disease states that feature involuntary weight loss and skeletal muscle atrophy. These states are generally characterized by altered BCAA availability (low BCAA intakes, elevated rates of BCAA oxidation, and gluconeogenesis), which are concurrent with activation of proteolysis and suppression of protein synthesis in skeletal muscle and ultimately lead to erosion of lean tissue mass. These features in turn imply BCAA deficiency compared with whole-body requirements and are the basis of suggestions for dietary supplementation with BCAA or their metabolites. Recent studies on BCAA supplementation in cancer focus on leucine and its derivative, beta-methyl beta-hydroxybutyrate, as regulators of skeletal muscle metabolism, although their relative efficacy is unknown. However, what would otherwise be a relatively straightforward consideration of amino acid supply and demand is confounded by the presence of the tumor and its potential utilization of BCAA for its proliferative and invasive activities. Positron emission tomography with (11)C-leucine, used for in vivo tumor imaging, points to the high avidity of tumor amino acid uptake. These features have incited research in opposing directions, probing BCAA deprivation, with a view to limiting tumor growth, as well as BCAA supplementation, with a view to supporting maintenance of host lean tissue. No clear conclusion is presently available from the sum of these efforts. Animal models with relevant clinical features are essential to determine if amino acid therapy can alter the balance between the host and the tumor in a manner that favors the host overall.

Effect of arginine-enriched total parenteral nutrition on the host-tumor interaction in cancer-bearing rats

By using a transplantable Yoshida sarcoma in a rat total parenteral nutrition model, we measured the effectiveness of an arginine-enriched amino acid solution (AI-82) in terms of leucine kinetics and nitrogen balance as indicators of host-tumor nutrition interaction compared with that of a conventional amino acid solution (Proteamin12). When tumor-bearing rats received isocaloric total parenteral nutrition solutions for 7 days, AI-82 significantly improved host nitrogen balance and significantly decreased the tumor-nitrogen trap throughout the experimental period. Leucine kinetics of whole body and tissues were also determined by a 4-hour continuous infusion of each total parenteral nutrition solution containing 14C-leucine. Significantly increased whole-body leucine oxidation (p < .01) without an increase in leucine release from normal tissues was observed in the AI-82 group. Total incorporation of 14C-leucine into whole muscle was significantly elevated (p < .05) without changes in muscle protein degradation in the AI-82 group. In the whole tumor, AI-82 tended to decrease total incorporation of 14C-leucine, but there was no difference in leucine release caused by protein breakdown between the two groups. These findings suggest that AI-82 can improve the nutritional status of the host over that of the tumor.

Optimum branched-chain amino acids concentration for improving protein catabolism in severely stressed rats

In this study, an experiment was performed to investigate the optimal concentration of branched chain amino acid (BCAA) in hyperalimentation to be administered when protein catabolism is accelerated by sepsis or bodily injury. Amino acid solutions containing BCAA 25%, 30%, 40%, 45% and 50% were prepared and were administered iv for three days with other essential amino acid-containing nitrogen in the same volume into rats with peritonitis which had been developed by ligature and puncture at the cecum, and the results were compared. After observing for three days, the influence over nitrogen balance, improvement of 3-methyl-histidine/creatinine in urine, weight loss in muscles, and aminogram in serum and muscles indicated that the hyperalimentation under stress is utilized most effectively when amino acid contains 45% of branched-chain amino acid.

Branched chain amino acids as the protein component of parenteral nutrition in cancer cachexia

A prospective randomized trial was conducted to determine the effects of branched chain amino acids (BCAA) as the protein component of total parenteral nutrition (TPN) on protein kinetics in patients with intraabdominal adenocarcinoma. Nine malnourished patients were given both conventional TPN containing 19 per cent BCAA (AA) and isocaloric, isonitrogenous TPN containing 50 per cent BCAA (BCAA-TPN), in random order. Both [13C]leucine and [14C]tyrosine were employed as tracers to avoid the potential bias due to the different amino acid composition of the two TPN solutions. With BCAA-TPN, leucine and tyrosine flux increased significantly from (mean +/- s.d.) 158.0 +/- 37.2 to 243.5 +/- 75.8 mumol kg-1 h-1 (P less than 0.025) and from 35.0 +/- 8.4 to 42.6 +/- 11.0 mumol kg-1 h-1 (P less than 0.05) respectively. Leucine oxidation was significantly higher on BCAA-TPN (24.1 +/- 6.3 on AA versus 68.3 +/- 37.1 mumol kg-1 h-1, P less than 0.025) while tyrosine oxidation was significantly lower (3.7 +/- 1.8 mumol kg-1 h-1 on AA versus 2.5 +/- 2.0 mumol kg-1 h-1 on BCAA-TPN, P less than 0.05). Whole body protein synthesis and breakdown was significantly higher on BCAA-TPN by the tyrosine tracer (31.3 +/- 7.3 on AA versus 40.1 +/- 9.3 mumol kg-1 h-1, P less than 0.025 and 33.0 +/- 8.4 on AA versus 41.3 +/- 11.1 mumol kg-1 h-1, P less than 0.05) respectively. Using the leucine tracers both synthesis and breakdown were increased, but not significantly, from 133.8 +/- 40.0 to 175.3 +/- 65.1 mumol kg-1 h-1 and from 127.9 +/- 33.6 to 167.7 +/- 71.2 mumol kg-1 h-1 respectively. The fractional albumin synthetic rate increased significantly on BCAA-TPN from 4.3 +/- 2.9 on AA to 8.0 +/- 5.1 per cent per day (P less than 0.05). The reduction in tyrosine oxidation, suggesting improved protein utilization, coupled with an increase in protein and albumin synthesis, strongly support a positive benefit from BCAA-TPN in cancer cachexia.

Improved protein kinetics and albumin synthesis by branched chain amino acid-enriched total parenteral nutrition in cancer cachexia. A prospective randomized crossover trial

A prospective randomized crossover trial was conducted to determine the effect of a branched chain amino acid (BCAA)-enriched solution on whole body leucine kinetics and fractional rates of albumin synthesis in patients with intra-abdominal metastatic adenocarcinoma. Ten malnourished cancer patients were provided isonitrogenous amounts of both a conventional total parenteral nutrition (TPN) formula containing 19% BCAA and a BCAA-enriched TPN formula containing 50% of the amino acids as BCAA in a random order. Whole body protein turnover was determined by a 10 hour continuous infusion of leucine 14C. Increased whole body leucine flux (68 +/- 5 mumols/kg BW/hr versus 145 +/- 11; mean +/- SEM; P less than 0.001) and oxidation (13 +/- 2 mumols/kg BW/hr to 46 +/- 5; P less than 0.001) were determined on the BCAA-enriched TPN. Increased whole body protein synthesis (2.2 +/- 0.2 g protein/kg BW/day versus 3.9 +/- 0.3; P less than 0.005) and leucine balance (2.5 +/- 0.4 g leucine/d versus 6.5 +/- 0.6; P less than 0.001) were also observed in patients receiving the BCAA-enriched TPN solution. Leucine release from protein breakdown was not statistically elevated (1.65 +/- 0.18 g protein/kg BW/d versus 2.48 +/- 0.40; P greater than 0.05) but, incorporation of leucine 14C into plasma albumin was significantly elevated (2.37 +/- 0.23 mumols/g/hr to 4.21 +/- 0.33; P less than 0.001) when the patients received BCAA-enriched TPN. Despite the better leucine balance, the improvement in the 24-hour urinary nitrogen balance was not statistically significant (6.6 +/- 3.9 g protein/d versus 11.4 +/- 2.9; control versus BCAA-enriched; P = 0.15). BCAA-enriched formulas improve whole body leucine kinetics, fractional rates of albumin synthesis, and leucine balance, and thus may favorably influence protein metabolism in cancer cachexia.