Effects of serum proteins on in vitro melamine-cyanurate crystal formation.

Melamine toxicity is recognized as a distinct form of renal failure due to occlusion of the renal tubules by the compound melamine and its deaminated derivative, cyanuric acid. The morphology of melamine-cyanurate crystals in vivo differs from that in vitro, being rounded in the former case but needle-like in the latter. The reasons for this difference in morphology between in vivo and in vitro crystals remain unknown. In the present study, we investigated the in vitro effects of several possible intra-renal factors, i.e., pH and serum and urinary proteins, on the morphology of melamine-cyanurate crystals in order to clarify what might be responsible for the formation of rounded urolites in vivo. We found that serum proteins, such as fetal bovine serum, bovine serum albumin and bovine gamma-globulin, can alter the morphology of melamine cyanurate, turning it into rounded crystals. The urinary protein beta-2-microglobulin had a less pronounced effect. The crystal morphology was unaffected by pH. Based on the present in vitro findings and known clinical data, we suggest a putative protein-related model for melamine-cyanurate formation in the kidney.