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 function in vitro. Incubation of confluent fibroblasts with EBT, but not its hydrolysis product 1-methyl-tetrahydro-beta-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 fibroblast, and suggest that EBT may be involved in the development of fibrosis in EMS.