Effects of twice‐daily ingestion of essential amino acids on amino acid transporter transcript and protein expression in older adults prior to total knee arthroplasty

Abstract

Following total knee arthroplasty (TKA) surgery, persistent muscle atrophy and weakness are the greatest clinical barriers to functional recovery. Essential amino acid (EAA) ingestion has been shown to be a potent stimulator of muscle anabolism and to acutely stimulate amino acid transporter mRNA and protein levels in muscle. We examined the effect of twice‐daily EAA supplementation on amino acid transporter gene expression and total protein levels. In this placebo controlled study muscle biopsies were obtained after an overnight fast, under anesthesia immediately prior to TKA surgery following seven days of twice‐daily ingestion of 20g EAA (n=9) or placebo (n=7). Biopsies were analyzed for transcript and protein expression of amino acid transporters using quantitative PCR and Western blotting and compared to placebo. Preliminary results indicate significantly higher mRNA levels for SNAT2 (p<0.01), SNAT4 (p<0.05), and LAT3 (p<0.01) and suggest trends toward increased mRNA for LAT1 (p<0.10) and PAT2 (p<0.10) and decreased mRNA for CAT2 (p<0.10). Total protein levels for CD98 and LAT1 were unchanged between groups. Total protein levels for CD98 and LAT1 were unchanged between groups. These preliminary data suggest EAA supplementation may up‐regulate amino acid transporters at the transcriptional level and regulation of these transporters may involve independent pathways. Support: NICHD K01HD057332