Effects of IL-1 muteins on cartilage degradation and as inducers of acute inflammation.

IL-1 peptides with N-terminal amino acid mutations were cloned and expressed to help characterize structural requirements for activity. Addition of Thr-Asn to the N-terminus (DP516) or substitution of the first two residues (Ala-Pro) of mature, native IL-1 beta with Thr-Met (DuP118) had no effect on the potency of the muteins in stimulating proteoglycan breakdown and inhibiting proteoglycan synthesis in vitro, or inducing mouse paw swelling in vivo. When Arg in position 4 of DuP118 was replaced by Glu (Glu-4), proteoglycan-synthesis-inhibitory activity was reduced to 20% and proteoglycan-degrading activity to 2% of that induced by native IL-1 beta. Glu-4 was much less active in inducing mouse paw swelling and gave maximal swelling about 40% that of native IL-1 beta. The data suggest that the presence of the positively charged side chain of Arg in position 4 may be important for the activity of IL-1 and may be useful in designing specific IL-1 receptor agonists/antagonists.