Differences in the cellular processing of Asp(B10) human insulin compared with human insulin and Lys(B28)Pro(B29) human insulin

Cellular metabolism studies were performed comparing human insulin with two rapid-acting analogs, Lys(B28)pro(B29) insulin (LysPro) and Asp(B10) insul in (B10-Asp). B10-Asp bound to isolated hepatocytes at 37 degrees C to a gr eater extent than LysPro or native insulin, which were equivalent. The rate of degradation was similar for the three materials, resulting in a signifi cant reduction in the degraded/bound ratio for the B10 analog. The processi ng of membrane-bound material was examined by incubating cells with hormone at 4 degrees C, removing unbound insulin, and incubating the cells at 37 d egrees C, Again, binding was greater for B10-Asp versus LysPro or native in sulin, with a reduction in the degraded/bound ratio. Hormone internalizatio n and processing was examined by an acid wash of cells incubated with I-125 (A14)-labeled hormone to remove surface-bound materials. The processing rat e was slower for B10-Asp versus LysPro or native insulin. Cell extraction a nd examination on molecular-sieve chromatography confirmed that B10-Asp was processed at a slower rate than either LysPro or native insulin. Intact B1 0-Asp was found in the cell after 4 hours, whereas all native insulin and L ysPro were degraded by 90 to 120 minutes. B10-Asp also caused a greater inc orporation of thymidine into DNA in cultured cells than LysPro or native in sulin, which were similar. These data show that the cellular processing of LysPro is essentially identical to that of native insulin. However, B10-Asp has markedly different properties and is processed much more slowly. The p rolonged cell residence time of B10-Asp could contribute to its greater eff ects on cell growth and mitogenesis. Copyright (C) 1999 by W.B. Saunders Co mpany.