1,1’-Ethylidene-bis-(L-tryptophan) is a potential impurity found in commercial preparations of L-tryptophan.1 It increases the proliferation of EoL-3 eosinophilic leukemia cells, release of eosinophil cationic protein from isolated human peripheral blood eosinophils, and IL-5 production in isolated human T cells.2 1,1’-Ethylidene-bis-(L-tryptophan) (40 µg/kg) induces fascia thickening and increases mast cell infiltration, inflammation, and fibrosis in superficial adipose and panniculus carnosus tissues in mice as a model system of eosinophilia-myalgia syndrome.3
1.Trucksess, M.W.Separation and isolation of trace impurities in L-tryptophan by high-performance liquid chromatographyJ. Chromatogr.630(1-2)147-150(1993) 2.Yamaoka, K.A., Miyasaka, N., Inuo, G., et al.1,1’-Ethylidenebis(tryptophan) (Peak E) induces functional activation of human eosinophils and interleukin 5 production from T lymphocytes: Association of eosinophilia-myalgia syndrome with a L-tryptophan contaminantJ. Clin. Immunol.14(1)50-60(1994) 3.Love, L.A., Rader, J.I., Crofford, L.J., et al.Pathological and immunological effects of ingesting L-tryptophan and 1,1’-ethylidenebis (L-tryptophan) in Lewis ratsJ. Clin. Invest.91(3)804-811(1993)