Proline Metabolism in Severely Burned Patients: Effect of Modulated Parenteral Feeding

The overall purpose of the study is to evaluate the effect of depleting proline supply in the nutritional support regimen on proline metabolism in the burn patients, this includes the rate of proline oxidation after burn injury, the rate of proline de novo synthesis from its immediate precursors glutamate and ornithine. The specific aims of the proposed study are: 1) to determine the kinetic status of proline metabolism and whole body proline balance under the following nutritional states: (a) "fasting; (b) regular total parenteral nutrition (TPN); (c)TPN with isonitrogenous depletion of proline, glutamate and ornithine metabolism under nutritional conditions studied in specific aim 1) above.

Proline is a non-essential amino acid. Its synthesis and catabolism is via the pathway of ornithine and glutamate, the latter two amino acids serve as its immediate precursors as well as metabolites. Ornithine is one of the intermediates for urea cycle, and glutamate is metabolically connected to tricarboxylic acid (TCA) cycle, the major cycle for energy production.

It is hypothesized that the significantly increased rates of net nitrogen loss and energy "production", as the consequence of the accelerated activities of both the urea and TCA cycles in burn injury "drain" both ornithine and glutamate, thus depleting tissues of the availability of proline. Hence, the de novo synthesis of proline is likely to be affected by the reduced availability of its major precursors: glutamate and ornithine.

This hypothesis is supported by 1) tissue and circulating glutamine content are reduced in stressed conditions; 2) ornithine disposal via oxidation is significantly increased after burn injury(2). Therefore, the availability of proline is likely to be limiting after burn injury for the synthesis of proteins. On the other hand, proline requirement is significantly increased in burn patients due to the high demand for tissue repair and wound healing. As a result, providing an adequate proportion of its precursors, glutamine / glutamate and / or as preformed proline, is of importance to maintain the appropriate supply and balance of amino acids for protein and other synthetic functions after burn injury.

The overall purpose of the study is to evaluate the effect of depleting proline supply in the nutritional support regimen on proline metabolism in the burn patients, this includes the rate of proline oxidation after burn injury, the rate of proline de novo synthesis from its immediate precursors glutamate and ornithine. The specific aims of the proposed study are: 1) to determine the kinetic status of proline metabolism and whole body proline balance under the following nutritional states: (a) "fasting; (b) regular total parenteral nutrition (TPN); (c)TPN with isonitrogenous depletion of proline, glutamate and ornithine metabolism under nutritional conditions studied in specific aim 1) above.

Eligibility Criteria:
Inclusion Criteria:

Burn patients being treated at MGH Burn Unit with one or more of the following criteria: 1) \>=5% TBSA; 2) inhalation injury; or 3) resting energy expenditure (REE) of \>15% of the predicted Basal Metabolic Rate using the Harris-Benedict equation.

Must be receiving total parenteral nutrition in the course of their treatment.

Exclusion Criteria:

Patients with thyroid disease. Patients who are not hemodynamically stable or show unstable vital signs Patients at the stage of major organ failure, e.g. renal and/or liver failure.