Selective inhibition of cyclooxygenase-2 by C-phycocyanin, a biliprotein from Spirulina platensis

We report data from two related assay systems (isolated enzyme assays and w hole blood assays) that C-phycocyanin a biliprotein from Spirulina platensi s is a selective inhibitor of cyclooxygenase-a (COX-2) with a very low IC50 COX-2/IC50 COX-1 ratio (0.04). The extent of inhibition depends on the per iod of preincubation of phycocyanin with COX-2, but without any effect on t he period of preincubation with COX-1. The IC50 value obtained for the inhi bition of COX-2 by phycocyanin is much lower (180 nM) as compared to those of celecoxib (255 nM) and rofecoxib (401 nM), the well-known selective COX- 2 inhibitors. In the human whole blood assay, phycocyanin very efficiently inhibited COX-2 with an IC50 value of 80 nM. Reduced phycocyanin and phycoc yanobilin, the chromophore of phycocyanin are poor inhibitors of COX-2 with out COX-2 selectivity. This suggests that apoprotein in phycocyanin plays a key role in the selective inhibition of COX-2. The present study points ou t that the hepatoprotective, anti-inflammatory, and anti-arthritic properti es of phycocyanin reported in the literature may be due, in part, to its se lective COX-2 inhibitory property, although its ability to efficiently scav enge free radicals and effectively inhibit lipid peroxidation may also be i nvolved. (C) 2000 Academic Press.