Time- and temperature-dependent stability of growth factor peptides in human autologous serum eye drops

Abstract

Purposes: To develop a step-by-step production method for human autologous serum (AS) eye drops that was broadly compliant with US Food and Drug Administration requirements for reinjection of processed biological substances. To determine optimum storage conditions for AS eye drops by measuring the concentration of growth factor peptides (GFP) as a function of storage temperature and storage duration.

Methods: AS derived from the blood of 3 healthy male volunteers was produced using a closed, vacuum-driven, cascade-filtration system under sterile, low-pyrogen conditions. In-process controls included methods for monitoring protein electrophoretic mobility and degradation rate and the content of free hemoglobin and endotoxin. Stability of transforming growth factor beta1, substance P, nerve growth factor, calcitonin gene-related peptide, insulin-like growth factor 1, and epidermal growth factor was evaluated at -15 degrees C, +4 degrees C, +25 degrees C, +37 degrees C, and +42 degrees C at different time intervals (hours to weeks). The main outcome measures were the concentrations of GFP, endotoxin, and lipid peroxidation by-products (a proxy measure for protein degradation) in dilute AS.

Results: The stability of GFP varies: transforming growth factor beta1, nerve growth factor, epidermal growth factor, and insulin-like growth factor 1 were more temperature and time resistant, but substance P and calcitonin gene-related peptide significantly degraded at +4 degrees C in 24 hours. Endotoxin and lipid peroxidation by-products were not significantly increased by processing.

Conclusions: This pilot study developed a closed, cascade-filtration system that was an effective method for the production of high-quality, low-pyrogen AS. The processing method broadly complied with Food and Drug Administration requirements for reinjection of biological substances. Variable GFP stability was observed at +4 degrees C and above. For clinical use, AS should be packaged in daily-use containers, which should be stored frozen; the container in active use should be refrigerated between doses.