Tear film MMP accumulation and corneal disease

Abstract

Background/aims: Matrix metalloproteinases (MMPs) accumulate in the tears of patients with active peripheral ulcerative keratitis (PUK) but it is unknown whether these enzymes have a central role in disease progression. The aims of the present investigation were to determine the source of these enzymes and to ascertain whether their accumulation in tears is a phenomenon specific to PUK or a general feature of other anterior segment diseases.

Methods: The experimental samples were obtained from the culture media of conjunctival and corneal epithelial cells, from fractionated blood plasma and leucocytes of healthy subjects and patients with rheumatoid arthritis, and from the tears of healthy subjects and patients with a variety of anterior segment diseases. The MMPs of all samples were visualised by zymography and tear samples were assayed using nitrophenol acetate and an MMP-9 susceptible quenched fluorescent peptide as substrate.

Results: The major MMPs that accumulate in the tears of patients with rheumatoid arthritis with active ocular disease are MMP-9 and a species of M(r) 116,000. By comparing the zymographic activity profiles of the gelatinases present in the samples obtained, it was deduced that the main source of these MMPs was granulocytes. Their accumulation in tears was not unique to patients with PUK; detectable amounts of the enzymes also occurred in the tears of patients with keratoconus with associated atopic disease, patients undergoing treatment for herpetic eye disease, and patients with systemic and non-systemic dry eye disease.

Conclusion: The MMPs that accumulate in tears are mainly derived from granulocytes. This may be effected by autoimmune diseases that involve ocular tissue or by ocular diseases that induce an inflammatory response.

Figure 1

Representative zymographic gelatinase activity profiles of the MMPs secreted by primary cultures of conjunctival cells (gel A, lanes 1 and 2) and corneal epithelial cells (gel B, lane 1: cultured in MEM medium; lane 2: cultured in high Ca²⁺ MEM medium which partially induces enzyme activation).

Figure 2

Representative zymographic gelatinase activity profiles of the MMPs produced by (A) granulocytes, (B) monocytes, (C) blood plasma, and (D) tears of patients with rheumatoid arthritis.