Suppression of granulopoietic progenitor cell proliferation by metabolites of the branched-chain amino acids.

The effects of branched-chain amino acid metabolites on granulocyte-macrophage progenitor cell proliferation in marrow culture are reported. Isovalerate and propionate profoundly suppress granulopoiesis at both 3.2 and 6.4 mM concentrations, whereas methylmalonate and other metabolites suppress to a lesser degree. The parent branched-chain amino acids leucine, isoleucine, and valine do not suppress in vitro granulopoiesis at similar concentrations. Because the concentrations of the organic acids tested fall within the pathophysiologic ranges observed in patients with isovaleric, propionic, and methylmalonic acidemias, we suggest that elevated in vivo levels of isovalerate, propionate, and to a lesser degree methylmalonate are responsible for the neutropenia observed in these disorders.