Enzymatic activity of visfatin/Nampt in synovial membrane of human osteoarthritis. Enzymatic activity of visfatin/nicotinamide phosphoribosyltransferase (Nampt) assayed in protein extracts of human osteoarthritis synovial membranes by colorimetric assay. Absorbance at 450 nm was measured every 5 minutes for 1 hour, representing the appearance of Nampt product, nicotinamide mononucleotide, over time. Negative control, water; positive control, recombinant visfatin/Nampt (50 μg/ml). Data are mean ± standard error of the mean of 3 samples. In parallel, recombinant visfatin/Nampt and two synovium samples were pretreated for 1 hour at 37°C with APO866 (10 nM). Histograms show the enzymatic Nampt activity displayed by the sample (per minute), calculated from the slope of the straight line of the curve, which is obtained by representing the absorbance (optical density) over time (per minute).