1,1'-ethylidenebis[L-tryptophan], an impurity in L-tryptophan associated with eosinophilia-myalgia syndrome, stimulates type I collagen gene expression in human fibroblasts in vitro

Eosinophilia myalgia syndrome (EMS), a recently described inflammatory disorder characterized by myalgia, peripheral eosinophilia, and multisystem inflammation is associated with L-tryptophan consumption. Fibrosis of various tissues due to excessive accumulation of type I collagen is a prominent late manifestation of the syndrome. 1,1'-Ethylidenebis [L-tryptophan] (EBT), an impurity distinct from L-tryptophan found in case-associated lots, has been implicated in the pathogenesis of EMS. We therefore investigated the effects of EBT on normal human fibroblast function in vitro. Incubation of confluent fibroblasts with EBT, but not its hydrolysis product 1-methyl-tetrahydro-β-carboline-3-carboxylic acid, caused a dose-dependent increase in collagen synthesis and in type I collagen mRNA levels independent of its effect on proliferation. In contrast, expression mRNA for fibronectin was not affected. These findings indicate that EBT stimulates type I collagen production by human fibroblasts, and suggest that EBT may be involved in the development of fibrosis in EMS.