Regulation of the pericellular activation of plasminogen and its role in tissue-destructive processes

A decade of silicone hydrogel development: surface properties, mechanical properties, and ocular compatibility

Since the initial launch of silicone hydrogel lenses, there has been a considerable broadening in the range of available commercial material properties. The very mobile silicon-oxygen bonds convey distinctive surface and mechanical properties on silicone hydrogels, in which advantages of enhanced oxygen permeability, reduced protein deposition, and modest frictional interaction are balanced by increased lipid and elastic response. There are now some 15 silicone hydrogel material variants available to practitioners; arguably, the changes that have taken place have been strongly influenced by feedback based on clinical experience. Water content is one of the most influential properties, and the decade has seen a progressive rise from lotrafilcon-A (24%) to efrofilcon-A (74%). Moduli have decreased over the same period from 1.4 to 0.3 MPa, but not solely as a result of changes in water content. Surface properties do not correlate directly with water content, and ingenious approaches have been used to achieve desirable improvements (e.g., greater lubricity and lower contact angle hysteresis). This is demonstrated by comparing the hysteresis value of the earliest (lotrafilcon-A, >40°) and most recent (delefilcon-A, <10°) coated silicone hydrogels. Although wettability is important, it is not of itself a good predictor of ocular response because this involves a much wider range of physicochemical and biochemical factors. The interference of the lens with ocular dynamics is complex leading separately to tissue-material interactions involving anterior and posterior lens surfaces. The biochemical consequences of these interactions may hold the key to a greater understanding of ocular incompatibility and end of day discomfort.

The appearance and possible role of plasminogen activator of urokinase type (u-PA) activity in the cornea related to soft contact lens wear in rabbits

This is the first study in which u-PA activity is detected in situ during SCL wear. The histochemical localization of u-PA activity is done by the methods of Lojda using unfixed cryostat sections on semipermeable membranes and a gel incubation medium containing sensitive substrates with the 7-amino-4-trifluoromethylcoumarin (AFC) (Enzyme Systems Products, Sierra Lane, Dublin, CA, USA) leaving groups. Z-Gly-Gly-Arg-AFC and Glut-Gly-Arg-AFC were employed as the substrates. The results show that in the normal,cornea u-PA activity is absent. Also the wearing of SCL does not evoke the appearance of u-PA activity in the cornea within the first three days. On day 4 the first u-PA activity appears; it is located in the superficial layers of the corneal epithelium. On day 7 of SCL wear, u-PA activity is present in all layers of the corneal epithelium and (to a lesser extent) also in the comeal endothelium; keratocytes of the corneal stroma are only slightly active for u-PA. Extended SCL wear (for two weeks) leads to an increase of u-PA activity in keratocytes beneath the epithelium. Also, some inflammatory cells (mainly polymorphonuclear leukocytes, PMNs) present in the corneal stroma are enzymatically active. After three weeks of SCL wear the number of PMNs in the corneal stroma increases; some PMNs are highly active for u-PA. In the corneal endothelium the u-PA activity is also highly pronounced. It can be concluded that extended SCL wear leads to the gradual increase of u-PA activity in the rabbit cornea. It is suggested that active u-PA is involved in the corneal damage related to SCL wear.

The proteolytic potential of normal human melanocytes: comparison with other skin cells and melanoma cell lines

To understand the contribution of epidermal melanocytes in the proteolytic potential of human skin, we have studied melanocytes grown in a low-serum medium deprived of phorbol esters, cholera toxin, and other non-physiological supplements. We focused on the plasminogen activation system and certain matrix metalloproteinases (gelatinases). Supposing that the proteolytic activity of cells can influence binding to collagen matrix and its reorganization, we have analyzed these parameters as well. We found that human melanocytes secreted tissue-type plasminogen activator and utilised it to generate cell-bound plasmin. No urokinase-type plasminogen activator was detected in the cultures but its receptor was found in cell extracts. Both the 72 kDa and 92 kDa gelatinases were secreted by the cells and in equal amounts. In addition, melanocytes secreted the wide-spectrum proteinase inhibitor alpha-2-macroglobulin. Melanocytes cast into collagen matrices retained a rounded morphology, did not extend processes, and were unable to contract collagen lattices. As a control, these parameters were investigated in parallel in cultures of human keratinocytes, dermal fibroblasts, and two melanoma cell lines. The obtained characteristics suggest that normal human melanocytes are proteolytically active cells. This function may pertain to skin physiology and pathophysiology.

Wound fluid from chronic leg ulcers contains elevated levels of metalloproteinases MMP-2 and MMP-9

The purpose of the present research was to determine if metalloproteinase levels were elevated in human chronic wound fluid. Samples of blood and wound fluid from acute (mastectomy) and chronic (leg ulcer) wounds were collected, and metalloproteinase profiles of the samples were determined by gelatin zymography. Compared to serum, acute wound fluid (mastectomy fluid) contained markedly increased levels (five-to tenfold) of several metalloproteinases including 72-kDa and 94-kDa gelatinases (MMP-2 and MMP-9). In chronic wound fluid, not only were these enzyme levels increased another five- to tenfold over mastectomy fluid, but also both activated enzyme and proenzyme species appeared to be present. Our results suggest that non-healing ulcers develop an environment containing high levels of activated metalloproteinases, which may result in chronic tissue turnover and failed wound closure.