Our studies have shown that MMP-9 is increased in wound fluids of diabetic patients, but the mechanism of this increase is not clear. MMP-9 activity is tightly regulated at many levels including by binding to Neutrophil Gelatinase-Associated Lipocalin (NGAL). NGAL is produced and secreted by neutrophils and can bind to MMP-9 to prevent its activation. We hypothesized that increased NGAL is in part responsible for the increase in MMP-9 activities in diabetic wounds. In this study we used an inflammatory wound sponge model to investigate the effect of diabetes on NGAL and its association with MMP-9 was also investigated.

Diabetes mellitus was induced in 17 male Sprague-Dawley rats (STZ:65mg/kg). Six weeks later 1cm² PVC sponges were implanted subcutaneously. Similarly treated non-diabetic age matched rats (n=9) acted as control. Three and six days after surgery the sponges were removed and the wound fluids and cells collected. Neutrophils in the infiltrate were counted by flow cytometry. TotalMMP-9 (pro+active forms) and NGAL-MMP-9 complex were measured by zymography and NGAL and MMP-9 mRNA levels by RT-qPCR.

Overall diabetes increased wound fluid totalMMP-9 and its activation (by 1.5 fold). At day 6 neutrophil number, NGAL mRNA and NGAL/MMP-9 complex were significantly increased but MMP-9 mRNA was not altered. These results suggest that increased wound neutrophil number and NGAL may contribute to the increased total MMP-9, thereby increasing MMP-9 activity. Whether this effect contributes to a delay in closure of excisional wounds remain to be established.  Supported by IPRS and NH&MRC.