The diurnal variation of matrix metalloproteinase-9 and its associated factors in human tears.
OBJECTIVE
Matrix metalloproteinases (MMPs) are degrading enzymes which maintain and remodel tissue architecture. Upregulation of MMP-9 has been associated with corneal erosions and ulceration. As these conditions are often exacerbated on waking, suggesting that degrading activity is upregulated overnight, this study set out to determine the diurnal variation of MMP-9, Tissue Inhibitor of Metalloproteinase (TIMP)-1, and Neutrophil Gelatinase-Associated Lipocalin (NGAL).


METHODS
Flush tears were collected from 46 healthy, non-contact lens wearers at midday, before sleep, and immediately on waking. Total protein content (TPC) was measured using the bicinchoninic acid method, and MMP-9, TIMP-1, and NGAL concentrations were measured using sandwich enzyme-linked immunoassay. Statistical analysis was performed using repeated measures analysis of variance.


RESULTS
TPC was 3.4 ± 1.5 mg/mL, 5.0 ± 3.7 mg/mL and 15.5 ± 8.4 mg/mL for midday, before sleep, and on waking respectively, the latter being significantly greater than the other two (P < 0.001). MMP-9 concentrations at the corresponding time points were 9.8 ± 14.3 ng/mL, 8.5 ± 11.7 ng/mL, and 2000.7 ± 1950.7 ng/mL. Again, the value on waking was significantly greater than the previous two visits (P < 0.001). TIMP-1 concentrations exceeded those of MMP-9 at midday but the ratio of the two reversed on awakening.


CONCLUSIONS
Concentrations of MMP-9 are negligible during the day and completely inhibited by TIMP-1. On awakening, MMP-9 increases 200-fold, an increase that is not completely inhibited by TIMP-1. This diurnal change, along with the presence of NGAL which protects MMP-9 from degradation, suggests that the closed eye is an environment conducive to extracellular matrix remodeling.
Brien Holden Vision Institute, Sydney, Australia. m.markoulli@brienholdenvision.org
Maria
M
Markoulli
Eric
E
Papas
Nerida
N
Cole
Brien A
BA
Holden
D000209:Acute-Phase Proteins / Q000378:metabolism*; D000293:Adolescent; D000328:Adult; D000704:Analysis of Variance; D015415:Biomarkers / Q000378:metabolism; D002940:Circadian Rhythm / Q000502:physiology*; D004797:Enzyme-Linked Immunosorbent Assay; D005260:Female; D006801:Humans; D000071068:Lipocalin-2; D054834:Lipocalins / Q000378:metabolism*; D008297:Male; D020780:Matrix Metalloproteinase 9 / Q000378:metabolism*; D008875:Middle Aged; D011446:Prospective Studies; D011518:Proto-Oncogene Proteins / Q000378:metabolism*; D015203:Reproducibility of Results; D013666:Tears / Q000201:enzymology*; D019715:Tissue Inhibitor of Metalloproteinase-1 / Q000378:metabolism*; D055815:Young Adult
D000209:Acute-Phase Proteins; D015415:Biomarkers; C489506:LCN2 protein, human; D000071068:Lipocalin-2; D054834:Lipocalins; D011518:Proto-Oncogene Proteins; D019715:Tissue Inhibitor of Metalloproteinase-1; D020780:Matrix Metalloproteinase 9