ACETALDEHYDE-INDUCED STIMULATION OF COLLAGEN-SYNTHESIS AND GENE-EXPRESSION IS DEPENDENT ON CONDITIONS OF CELL-CULTURE - STUDIES WITH RAT LIPOCYTES AND FIBROBLASTS

Acetaldehyde has been proposed as a mediator of fibrogenesis in alcoho lic liver disease, based in part on its ability to stimulate collagen synthesis by hepatic lipocytes in rate primary or passaged culture. In this study, we examined the effect of acetaldehyde on rat lipocytes a nd fibroblasts at various stages of culture, in an effort to determine whether culture-related events influence responsiveness to this compo und. Lipocytes from normal rat liver were studied in primary culture a t 3 and 7 days after plating; fibroblasts were studied in subculture, at subconfluent and confluent densities. Both cell types were incubate d with 100 mu M acetaldehyde for 24 hr followed by measurement of coll agen synthesis and type I collagen gene expression. Acetaldehyde had n o effect on lipocytes at either 3 or 7 days in primary culture. The in ability of acetaldehyde to stimulate collagen synthesis in primary cul ture was not attributable to toxicity, because cell morphology and tot al protein synthesis were identical in both treated and untreated cult ures. Fibroblasts exhibited a variable response to acetaldehyde that w as dependent on cell density: subconfluent cells contained similar amo unts of type I collagen mRNA in both the presence and absence of aceta ldehyde, whereas confluent cells exhibited a 2- to 3-fold increase in collagen mRNA levels upon acetaldehyde exposure. To determine whether quiescent lipocytes would respond to acetaldehyde in a culture system that mimics the hepatic environment in vivo, lipocytes were plated in coculture with hepatocytes on a basement membrane gel and incubated wi th 20 mM ethanol for 72 hr. Direct communication between these two cel l types did not provoke lipocyte activation, even in the setting of et hanol oxidation. We conclude from these experiments that acetaldehyde is not a primary stimulus to lipocyte activation in vivo. Acetaldehyde may enhance collagen synthesis by lipocytes, but its activity appears restricted to cells that have undergone a prior priming event in cult ure or in vivo. Of the many phenotypic changes that occur in lipocytes during the first week of primary culture, none sensitizes them to the fibrogenic effects of acetaldehyde.