4.10. Soluble Sirius Red Assay

Collagen content in CF was measured as described previously [40]. Briefly, CFs were stimulated with the indicated compounds for 72 h. Afterward, the culture medium was discarded, and the cells were fixed with 4% paraformaldehyde (Roth). To stain the collagen, cells were incubated with 0.1% Sirius red F3B dye (BDH Laboratory Supplies, Poole, UK) in 0.01 M HCl for 1 h. After extensive washing with 0.01 M HCl, the dye was dissolved in 0.01 M NaOH and absorbance was measured at OD550 in a microplate reader (EL808, Bio-Tek, Winooski, VT, USA). OD values were compared to a gelatin standard curve.