[CD34 and alpha-smooth muscle actin expression of keratocytes following photodynamic inactivation (PDI)]

Photodynamic inactivation (PDI) may be a potential treatment alternative in therapy-resistant infectious keratitis. PDI may eliminate the microorganisms from the infected cornea by damage caused through free oxygen radicals, or even by supporting different stages of activation of keratocytes and inflammatory cell response. The purpose of this study was to determine the impact of PDI on activation of human keratocytes in culture.

Primary human keratocytes were isolated by digestion in collagenase A (1 mg/mL) from human corneal buttons, and cultured in DMEM/Ham's culture medium supplemented with 10% foetal calf serum. Keratocytes underwent illumination (670 nm) for 13 minutes following exposure to 0, 50, 150 and 250 nMol/ml concentrations of the photosensitizer chlorin e6 (Ce6) in the culture medium. Twenty-four hours after treatment CD34 and α-smooth-muscle actin expression of the cells was analysed using flow-cytometry (FACS).

Using Ce6 or illumination only, α-smooth-muscle actin expression of the cells did not change significantly. Twenty-four hours after PDI the percentage of CD34-positive keratocytes did not change significantly using 50-250 nM Ce6, however, the percentage of α-smooth-muscle actin-positive keratocytes decreased significantly at 250 nM Ce6 (p = 0.01).

As a short-term effect, PDI seems to inhibit myofibroblastic transformation of keratocytes, but does not have an impact on activation of CD34-positive keratocytes.With this impact PDI possibly may reduce the antimicrobial defence of keratocytes.