The effect of rhodium and copper analogs of cobalamin on human cells in vitro

Rhodium and copper analogs of various cobalamins have been found to produce an anti-vitamin B 12 effect in bacteria, leading us to see if similar inhibitory activity could be demonstrated for human cells. The analogs competed effectively with cyanocobalamin for binding by human serum transcobalamins. Methylrhodibalamin and 5′-deoxyadenosylrhodibalamin also competed with cyanocobalamin for serum-mediated uptake by human blood cells and bone marrow cells, though the competition was relatively weak when compared to the effective competition for transcobalamin II binding. None of the analogs affected normoblastic bone marrow cells, using deoxyuridine suppression of [ 3H]thymidine incorporation into DNA as the index of vitamin B 12 sufficiency. In fact, methylrhodibalamin actively corrected the abnormality in vitamin B 12-deficient bone marrow. However, 5′-deoxyadenosylrhodibalamin worsened the vitamin B 12-deficient behavior of megaloblastic bone marrow and inhibited its correction by vitamin B 12 and may even have adversely affected one of the five normoblastic marrows tested.