Inhibitory effects of plasma dialysate on protein synthesis in vitro: influence of dialysis and transplantation.

An in vitro technique was designed to measure the protein synthesis rate in the presence of plasma dialysate from severely uremic patients. Some of them were treated with a poor nitrogen diet, hemodialysis, or transplantation. The data observed with plasma of such patients were compared to those obtained with plasma dialysate of control subjects. Each plasma sample was dialyzed for 24 hr to extract the molecules having molecular weights less than 12,000 and the dialysate was lyophilized. Protein synthesis was studied in vitro, using a cell-free system from mouse Krebs II ascites cells. The cells were lysed, and the 30,000 x g supernatant (“5-30 lysate”) was used to test the protein synthesizing activity of the plasma dialysate from control and uremic animals. The rate ofprotein synthesis was monitored by measuring the incorporation ofa radiolabel (3H-leucine) into trichloroacetic acid-precipitable material in the presence of increasing amounts of plasma dialysate. In the presence of dialysate plasma from uremic patients as well as from hemodialyzed (HD) patients sampled before dialysis, there was a decrease in the 3H-leucine incorporation rate when the amount of added dialysate increased in the incubating medium. In severely uremic patients a difference between a high or low nitrogen diet could not be demonstrated. Though the count level of incorporated leucine with plasma from HD patients was always lower than that recorded in the presence of non-HD patients, the difference was not significant. However both these incorporation curves were significantly lower than the control curve (P < 0.01). Plasma specimens from HD patients were obtained at the beginning and end of a dialysis session. The comparison between the preand postdialysis incorporation curve showed an obvious improvement in the leucine incorporation rate with postdialysis plasma dialysate. In all transplanted patients but one, the incorporation curve was similar to the control curve. Therefore, it could be concluded 1) that uremic plasma inhibits protein synthesis, 2) predialysis plasma has the same inhibitory effect on in vitro protein synthesis as plasma from non-HD patients, 3) dialysis removes a great part of this inhibitory effect which appears to be related to dialyzable molecules, and 4) successful transplantation restores a normal pattern of in vitro protein synthesis. Am. J. Clin. Nutr. 33: 1407-1410, 1980. The alterations of protein metabolism in renal failure have been reviewed elsewhere (1, 2). They may be related to the prescription of poor protein diet and/or to the abnormal accumulation of “uremic toxins” in the patient’s blood. In previous studies in chronically uremic children, we have demonstrated the occurrence of changes in muscle cell protein metabolism. These included a decrease in the amount of the noncollagenous proteins (“alkali soluble proteins”) (3) and an increase of the free amino acid pool associated with modification in its qualitative composition (4). These alterations were more accentuated in patients treated with low nitrogen diets and in children undergoing long-term hemodialysis. More recently, we have demonstrated an inhibitory effect of uremic ultrafiltrate on in vitro protein synthesis (C. Dclaporte and F. Gros, unpublished observation). The purpose of this study was to investigate the effects of plasma dialysate on the in vitro protein synthesis in the presence of plasma obtained from uremic patients 1) receiving a low or high protein diet, 2) treated with hemodialysis, and 3) after transplantation.