Amelioration of the protein metabolic response in spermidine-supplemented trauma rats

Polyamines are biologically active, small, positively charged ubiquitous compounds that play an important role in initiating adaptive changes in cell proliferation, cell growth, and synthesis of proteins and nucleic acids. The potential for exogenous dietary polyamine to significantly contribute to whole-body growth and health has not been explored. This study evaluates the efficacy of feeding a liquid diet supplemented with 0.05% spermidine in injured rats. Rats traumatized by bilateral femur fracture (n = 12) and pair-fed uninjured controls (n = 12) were starved for 2 days and then refed for 4 days with a liquid diet containing 0.05% spermidine or an isonitrogenous control diet. Daily urine and body weight data were collected. At the end of refeeding, the rats were killed, and blood, cerebrospinal fluid (CSF), muscle, and brain tissue were collected. Spermidine supplementation (0.05%) was found to be tolerated well by the rats and (1) did not affect voluntary food intake by traumatized rats, (2) did not alter the growth rate, (3) increased protein utilization efficiency, and (4) decreased leucine, isoleucine, and valine levels in plasma and muscle. The profound effect of trauma on plasma amino acid metabolism seen in rats fed the basal diet was absent in spermidine-supplemented rats. Depletion of plasma glutamine (GLN) levels due to trauma was significantly less in rats with spermidine supplementation (11% v 33%), indicating a beneficial effect to counteract trauma responses. The results suggest that spermidine supplementation improves protein utilization efficiency and ameliorates trauma effects on amino acid levels.