The nutraceutical flavonoid luteolin inhibits ADAMTS-4 and ADAMTS-5 aggrecanase activities

A disintegrin and metalloprotease with thrombospondin domains (ADAMTS)-4 (aggrecanase-1) and ADAMTS-5 (aggrecanase-2) are metalloproteases involved in articular cartilage degradation and represent potential therapeutic targets in arthritis treatment. We explore herein the ability of different natural compounds to specifically block the destructive action of these enzymes. Following a preliminary screening using carboxymethylated transferrin as substrate, we focused our interest on luteolin due to its inhibitory effect on ADAMTS-4 and ADAMTS-5 activities using aggrecan and fluorogenic peptides as substrates. However, matrix metalloproteinases (MMPs) activities on these substrates result less affected by this flavonoid. Moreover, incubation of mouse chondrogenic ATDC5 cells in the presence of luteolin clearly decreases the release of aggrecan fragments mediated by aggrecanases under the same conditions in which aggrecanolysis mediated by MMPs is detected. Additionally, glycosaminoglycan levels in culture medium of murine cartilage explants stimulated with interleukin-1-alpha plus retinoic acid are reduced by the presence of the flavonoid. This inhibition takes place through blockade of ADAMTS-mediated aggrecanolysis, while MMPs activity is not or poorly affected. These results suggest that luteolin could be employed as a prototypic modifying disease-agent to create new chondroprotective compounds aimed to specifically block the unwanted aggrecanase activities in arthritic diseases.