Intraocular lenses

Minimum endotoxin concentration causing inflammation in the anterior segment of rabbit eyes

PURPOSE

This was a quantitative study to investigate the minimum endotoxin concentration causing inflammation in the anterior segment of the eye.

METHODS

Endotoxin was injected intracamerally in pigmented rabbits. A quantitative determination of flare and cells in the aqueous was performed using a laser flare-cell photometer, before and until 72 h after the treatment. An area under the curve (AUC) analysis was employed to evaluate the whole inflammatory reaction regarding flare values.

RESULTS

The time course of flare values in each endotoxin group showed a similar pattern with a peak value at 3 h. An AUC corresponding to values for "average +2sigma", 19301.8 in control eyes, was considered the cutoff value. Using this cutoff value and the regression curve in endotoxin-treated groups, the minimum endotoxin concentration causing inflammation regarding flare values was determined to be 0.60 endotoxin units (EU). Cell counts (cells/0.5 mm(3).0.5 s) corresponding to the value "average +2sigma", 6.07 at 24 h, in control eyes was considered to be the cutoff value. The minimum endotoxin concentration regarding cell counts was determined to be 0.23 EU.

CONCLUSION

There was a dissociation in response between flare and cells in the aqueous to intracameral endotoxin. The minimum endotoxin concentration causing inflammation ranged between 0.23 and 0.60 EU.

One-step surface modification of poly(lactide-co-glycolide) microparticles with heparin

PURPOSE

The aim of this study was to modify the surface of poly(lactide-co-glycolide) (PLGA) microparticles with heparin. The heparin-coated PLGA may enhance blood and tissue compatibility of PLGA devices and provide a novel approach to deliver growth factors.

MATERIALS AND METHODS

A one-step method using heparin to replace traditional emulsifiers (e.g., PVA) during emulsion-solvent evaporation process was employed to surface-entrap heparin in PLGA microspheres. The emulsifying activity of heparin was modified via varying counter ion form, including univalent (Na(+), K(+), Li(+), and [Formula: see text]) and divalent (Ca(2+), Mg(2+), Ba(2+), and Zn(2+)) cations, and complexation with amino acids (Arg, Lys, Leu, Val, Gly and Glu). Surface accessible and total heparin loading were determined by a modified toluidine blue assay and elemental analysis, respectively.

RESULTS

Heparin bound with univalent counter ions and amino acids exhibited emulsifying activity to varying degrees, whereas divalent heparin salts tended to cause complete aggregation of the PLGA o/w emulsion. Increasing pH (>or=7.4) of hardening medium enhanced heparin adsorption and significantly stabilized the PLGA o/w emulsion. The initial surface density of heparin on the PLGA microspheres prepared using univalent heparin salts was around 8-33 mg/m(2). Surface associated heparin desorbed quickly; potassium heparin showed the best retention, with approximately 0.2 and 0.1 mg/m(2) detected on PLGA microsphere surface following 1- and 14-day incubation in PBST at 37 degrees C, respectively.

CONCLUSIONS

PLGA microparticles were successfully surface-modified with heparin. Univalent salts and amino acid complexes of heparin, as effective emulsifiers, can become surface-immobilized in PLGA microspheres.