Suppression proliferation amino acids of granulopoietic progenitor cell by metabolites of the branched-chain 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. (J PEDIATR 106:62, 1985) Raymond J. Hutchinson, M.D., Kirsten BunneU, B.S., and Jess G. Thoene, M.D. Ann Arbor, Michigan INBORN ERRORS of branched chain amino acid metabo- lism result in the accumulation of various organic acid intermediates and are clinically associated with neutrope- nia during acute exacerbations of these disorders. The four disorders most commonly associated with neutropenia are isovaleric acidemia, /3-ketothiolase deficiency, propionic acidemia, and methylmalonic acidemia? ,2 The cause of neutropenia in these disorders is poorly understood. The inhibition of granulopoiesis by amino acid metabo- lites and other organic molecules has not been widely investigated. Inoue et al. 3 have reported the in vitro inhibition of bone marrow stem cell growth by methylma- Ionic acid. In addition, Meagher et al. 4 reported that the From the Department of Pediatrics, University of Michigan Medical School. Supported in part by Grant AM25548 from the National Insti- tutes of Health; the Michigan Department of Mental Health Genetic Screening Program; and Medical Service Grant Cv376 from the National Foundation-March of Dimes. Presented in part at the Annual Meeting of the Society for Pediatric Research, Washington, D.C., May 1983. Submitted for publication April 25, 1984; accepted June 1, 1984. Reprint requests: Raymond J. Hutchinson, M.D., Pediatric Hematology, Mott F6515, Department of Pediatrics, 1405 E. Ann St., Ann Arbor, MI 48109. small organic molecules ethanol and acetaldehyde inhibit- ed hematopoietic progenitor cell proliferation. With the development of in vitro techniques for the growth of bone marrow progenitor cells it has become possible to investi- gate the factors influencing progenitor cell proliferation. We used a semisolid culture method to assess the effects of various metabolites of the branched-chain amino acids on neutrophil precursor proliferation. CFU-GM IC5o Colony-forming unit- granulocyte/macrophage Concentration producing 50% inhibition METHODS Marrow donors. During the course of the experiments 21 individual bone marrow samples from 20 donors were obtained. Sixteen of the marrow specimens were collected from normal adult donors after obtaining written informed consent. The consent form was approved by the Committee to Review Grants for Clinical Research and Investigation Involving Human Beings of The University of Michigan. Five of the marrow specimens were harvested from patients with cancer not involving the marrow, at the time of a clinically indicated marrow aspiration. Marrow preparation. The marrow specimens were dilut- ed 2:1 to 3:1 with modified McCoy 5A medium and 62 The Journal of P E D I A T R I C S