Inhibitor of marrow thymidine incorporation from sera of patients with uremia.

A low-molecular-weight fraction of serum samples from 14 patients with uremia inhibited tritiated thymidine incorporation (18 +/- 2%) by cultured rabbit marrow whereas an identical fraction from nonazotemic subjects did not. A similar effect on ferrous 59 incorporation into heme was observed. A significantly smaller inhibition (8 +/- 2%) was noted in serum samples from patients on maintenance dialysis. The fraction containing inhibitory activity was filterable through a membrane that had a nominal mol-wt cutoff at 10,000 daltons (Amicon UM-10) and was retained wholly or in part on a membrane that had a 500-dalton cutoff (UM-05). On Sephadex G-50 and G-15 filtration, the inhibitory substance appeared in the first absorbance peak. This substance from 2 patients maintained on dialysis was studied further for its inhibitory activity. Dose-responsiveness was noted. The inhibitor was stable when it was heated to 56 degrees C for 60 min, but the activity was lost immediately when it was heated to 100 degrees C. Significant inactivation was observed following incubation with protease and papain. The inhibitor was partially soluble in chloroform. Taken together, these data suggest that uremic serum contains an inhibitor of marrow DNA synthesis in vitro, which may consist of peptides with mol wt less than 10,000 daltons and probably greater than 1,000 daltons. PTH or a mixture of urea, creatinine, methylguanidine, and guanidosuccinic acid did not show such inhibition on the marrow. This in vitro system offers a simple and reproducible method of testing various fractions of serum to allow further characterization of some toxic materials in uremic serum.