Serum albumin, serum antiproteases and polymorphonuclear leucocyte neutral collagenolytic protease in the tear fluid of normal healthy persons

Comparative proteome analysis of the tear samples in patients with low-grade keratoconus

PURPOSE

To elucidate the metabolic processes playing roles in the formation of keratoconus (KC).

METHODS

Tears samples were collected using capillary glass tubes without stimulation and without prior anesthesia from 17 patients and 16 controls. Proteomic analysis by fluorescent 2D gel electrophoresis (DIGE) coupled with MALDI-TOF/TOF was performed. The identified proteins that were differentially regulated were subjected to Ingenuity Pathway Analysis (IPA). Corneal topography analyses with Sirius topography system (Costruzioni Strumenti Oftalmici, Florence, Italy) were performed on all participants. The steepest keratometry index was lower than 50 diopters in all keratoconus patients.

RESULTS

DIGE analysis showed changes in abundance of nine proteins. Six of these proteins, namely serum albumin, Keratin Type II Cytoskeletal 1, IgG gamma chain-1, GAPDH, alpha-1 antitrypsin and ApoA-I, were down-regulated in the KC samples in comparison with the controls. In addition, we detected up-regulation of lysozyme C, keratin type I cytoskeletal 10 and lipocalin. The subsequent IPA predicted that NADH repair pathway is activated in the KC patients. This pathway involves generation of NADHX as a by-product via catalysis by GAPDH. NADHX is an inhibitor of several dehydrogenases and must be removed.

CONCLUSION

The involvement of NADHX repair pathway in KC should be investigated, since preliminary clues obtained in this study point to that direction. In particular, showing the presence of ATP-dependent NAD(P)H-hydrate dehydratase that eliminates NADHX would strengthen our findings and would be a major step toward understanding KC.

In-depth analysis of the human tear proteome

The tears, a critical body fluid of the surface of the eye, contain an unknown number of molecules including proteins/peptides, lipids, small molecule metabolites, and electrolytes. There have been continued efforts for exploring the human tear proteome to develop biomarkers of disease. In this study, we used the high speed TripleTOF 5600 system as the platform to analyze the human tear proteome from healthy subjects (3 females and 1 male, average age: 36±14). We have identified 1543 proteins in the tears with less than 1% false discovery rate, which represents the largest number of human tear proteins reported to date. The data set was analyzed for gene ontology (GO) and compared with the human plasma proteome, NEIBank lacrimal gland gene dataset and NEIBank cornea gene dataset. This comprehensive tear protein list may serve as a reference list of human tear proteome for biomarker research of ocular diseases or establishment of MRM (Multiple Reaction Monitoring) assays for targeted analysis. Tear fluid is a useful and an accessible source not only for evaluating ocular surface tissues (cornea and conjunctiva), inflammation, lacrimal gland function and a number of disease conditions, such as dry eye as well as response to treatment.

Identification, origins and the diurnal role of the principal serine protease inhibitors in human tear fluid

PURPOSE

Previous work identified polymorphonuclear leukocyte (PMN) elastase as the major caseinolytic entity in tears collected after overnight eye closure. This study was designed to identify the principal serine protease inhibitors (serpins) in tears and to determine their function in the regulation of PMN cell proteases on eye closure.

METHODS

Reflex and closed eye tear samples were collected by microcapillary tube and centrifuged. After reflex and closed eye supernatants (R and C) were fractionated by HPLC, samples were subjected to casein zymography and reverse zymography. Western blots were utilized to screen tears and HPLC fractions for elastase, cathepsin G and proteinase-3 and to obtain semi-quantitative data on alpha 1-protease inhibitor (alp1), alpha 1-antichymotrypsin (alpha 1-Achy), secretory leukocyte protease inhibitor (SLPI), elafin and alpha 2-macroglobulin (alpha 2-M) as well as associated complexes and products. To confirm specificity of reactivity, samples were immunoprecipitated for a given protease or serpin and screened for the coprecipitation of interacting species.

RESULTS

Although R fluid contains no caseinolytic activity, it contains low levels of serpin-like activity principally in the form of SLPI (5-10 ng/microliter). Lesser amounts of alpha 2-M, alpha 1-Achy and alp1 (approximately < 1-3 ng/microliter) are also evident. C fluid is associated with very high levels of PMN cell proteases along with a approximately 5-20-fold increase in the concentrations of all of the above inhibitors. Trace levels of elafin were also detected. The concentrations of rapid reacting inhibitors exceeded that of proteases, with SLPI, alpha 1-Achy and alp1 being the principal functional entities. In atypical samples, complexes of elastase and alpha 2-M were also encountered.

CONCLUSIONS

SLPI, a known antimicrobial agent and an elastase and cathepsin G inhibitor, is the principal serpin in R fluid. C fluid is associated with a marked increase in the concentrations of an array of rapid reacting serpins capable of inhibiting all known PMN cell serine proteases. In the normal closed eye, the concentration of rapid reacting inhibitors always exceeds that of proteases with C fluid also containing a functional reserve of the slow reacting inhibitor alpha 2-M.

Lactoferrin and serum albumin in the conjunctival fluid of eyes operated for senile cataract

The concentrations of serum albumin (SA) in the conjunctival fluid were measured in 25 patients before surgery and in the post-operative period following cataract extraction. We found a significant increase in mean tear fluid SA concentration on the first post-operative day. The SA concentration remained high during the first 3 pre-operative levels. No correlation between the post-operative concentration profile of tear fluid SA and earlier findings of the tear lactoferrin (LF) profile of the same group of patients (Jensen et al. 1985) could be shown, although a trend towards an inverse relationship was apparent from the graphs. Pre-operatively, we found a significant positive correlation between age and concentration of SA in the conjunctival fluid (P less than 0.05) which might be interpreted as an increase in leakage from conjunctival vessels with age. This would, at least partly, explain the decreasing LF concentration with age (Jensen et al. 1986; McGill et al. 1984). It is concluded that transudate/exudate from the conjunctival vessels, represented by the change in the SA concentration in the conjunctival fluid, might be responsible for an initial post-operatively reduced concentration of LF and possibly other lacrimal gland proteins.

Lacrimal and salivary secretion in Sjögren's syndrome: the effect of systemic treatment with bromhexine

In a randomized clinical study, 32 patients with Sjögrens syndrome (SS) were given placebo/bromhexine (Bisolvon) 48 mg daily for 3 weeks. Various ophthalmological and oral variables as well as different proteins in tear fluid and saliva were registered. Bromhexine stimulated the tear secretion significantly, presumably without changing the protein composition of the tear fluid. In saliva the IgM concentration in contrast to other proteins decreased in patients with high pre-treatment values. Bromhexine may be of valuable help in the treatment of some patients with SS.

Serum antiproteases and polymorphonuclear leucocyte neutral collagenolytic protease in the tear fluid of patients with corneal ulcers treated with n-butylcyano acrylate glue

Four patients with central melting perforating corneal ulcers were treated by n-butylcyano acrylate gluing of the ulcer region. The glue facilitated healing of the eyes, and when the glue scaled off weeks later the corneas were left with stable leucomas. The glue membrane appears to prevent tear-borne polymorphonuclear leucocytes (PML) from reaching the ulcer region and to diminish activation of PML, with the consequent dramatic fall in tear fluid polymorphonuclear leucocyte neutral collagenolytic protease (PML-c-ase). After gluing, the tear fluid content of serum antiproteases returns to normal levels within days. This might indicate a decreased leakage of proteins from conjunctival vessels.