Fibroproliferation in liver disease: Role of monocyte factors

Fibroproliferation was measured as the uptake of [³H]thymidine into fibroblasts. Human fibroblasts were incubated with 200 μl monocyte‐conditioned medium, the 0.22 μm filtrate from cultured monocytes, in Dulbecco's modified Eagle medium supplemented with controlled process serum replacement 2, a fetal calf serum substitute with low mitogenic activity. Increasing the numbers of fibroblasts resulted in a parallel increase in thymidine uptake to a maximal level. Fibroblasts (2 × 10³) were plated into microwell plates and incubated with monocyte‐conditioned medium for 72 hr. At 16 hr before harvest, 1 μCi [³H]thymidine was added. Cells were harvested with phosphate‐buffered saline and washed, and the filters were counted. Fibroblasts incubated with Dulbecco's modified Eagle medium and controlled process serum replacement 2 showed minimal thymidine uptake. Fibroblasts incubated with Dulbecco's modified Eagle medium plus monocyte‐conditioned medium from monocytes stimulated with 10 μg/ml lipopolysaccharides showed a sixfold increase in thymidine uptake over fibroblasts in Dulbecco's modified Eagle medium and controlled process serum replacement 2 alone. Fibroblasts incubated with Dulbecco's modified Eagle medium plus monocyte‐conditioned medium from monocytes of patients with liver disease (n = 20) showed a 10‐fold elevation in thymidine uptake compared with Dulbecco's modified Eagle medium and controlled process serum replacement 2. Results indicated that preincubation of monocyte‐conditioned medium with either anti‐interleukin‐1β (12.5 halfmaximal units, 4° C, 16 hr) or catalase (1,870 IU, 25° C, 1 hr) did not alter the fibroproliferative activity of the monocyte‐conditioned medium, suggesting that neither interleukin‐1β nor activated oxygen intermediates were involved in fibroproliferation. Fibroblasts were incubated with platelet‐derived growth factor in increasing concentrations to produce a dose‐response relationship. Platelet‐derived growth factor was found to significantly enhance fibroproliferation. The addition of antibody to platelet‐derived growth factor reduced the fibroproliferation activity of plateletderived growth factor. Samples of monocyteconditioned medium were then preincubated with anti—platelet‐derived growth factor to determine whether platelet‐derived growth factor in the monocyte‐conditioned medium was mediating fibroproliferation. Anti—platelet‐derived growth factor reduced the fibroproliferative activity of the monocyteconditioned medium, suggesting that platelet‐derived growth factor probably plays a role in the fibroproliferation observed with monocyte‐conditioned medium obtained from patients with liver disease. (HEPATOLOGY 1992;15:191–197).