MMP3 and Arthritis: In line with this, our observation that the MMP3 serum concentrations were above the detection limit in both diet groups with and without arthritis induction and not only in the normal iron diet group with arthritis induction indicates that the arthritis-mitigating effect of the hypoferric state may be mediated by interference with the cytokine-like signaling activities of TIMP-1 and take place independently from matrix metalloproteinase activities.