Comparison of the biological stability of liposome-encapsulated nerve growth factor at different depot stages

Tianrun Lü; Jun LIU; Xiaojian CAO; Qi CHEN; Suqin LI

ABSTRACT

BACKGROUND:

Nerve growth factor (NGF) is characterized by poor stability both in vitro and in vivo, and liable to lose its bioactivity.

OBJECTIVE:

To study the stability of liposome-encapsulated NGF injection preserved under various conditions.

DESIGN:

A controlled study of liposome-encapsulated NGF.

SETTING:

Department of Surgery of the First Affiliated Hospital of Nanjing Medical University.MATERIALS This study was carried out at the Central Laboratory of the First Affiliated Hospital of Nanjing Medical University between July 2002and March 2004. NGF from rat submaxillary gland was purified, encapsulated by liposome, and prepared into lyophilized dosage form before preserved under different conditions (at 4 ℃, room temperature, 40 ℃ or 40 ℃ with saturated humidity, respectively).

METHODS:

Chicken embryo dorsal root ganglion cultured in serum-free medium was used to evaluation the bioactivity of NGF in vitro. The dorsal root ganglion from 8-day-old chicken embryo was inoculated in a polylysine-coated 24-well culture plate and cultured in Dulbecco modified Ea-gle medium (DMEM) containing different testing samples. Only DMEM was used for culture in the negative control group, while DMEM containing NGF at different concentrations used in the positive control group. The ganglion was cultured at 37 ℃ with 50 mL/L CO2 and saturated humidity for 24 hours, and the growth of the nerve fibers was observed under an inverted microscope. The bioactivity of NGF was also evaluated in simulated condition in vivo by adding lyophilized liposome-encapsulated NGF and positive control NGF specimen into 0.5 mL rat serum, which, along with the blank control serum, was added into 2.5 mL DMEM at 0.5, 1, 2, 3, 4,6 hours and thoroughly mixed. The bioactivity of NGF was assessed accord-ing to the length and density of the dorsal root ganglion and graded the prominences (recorded as "++" or "+++ "), and very long and dense growth of the prominences (++++).MAIN OUTCOME

MEASURES:

In vitro bioactivity of NGF preserved for 10, 30, 60, and 90 days by testing the growth of cultured chick embryo dorsal root ganglion in serum-free DMEM and in test of rats serum containing NGF added at 0, 0.5, 1, 2, 3, 4, and 6 hours into DMEM.

RESULTS:

Lyophilized liposome-encapsulated NGF exhibited stable bioactivity (+++) after preservation at 4℃ and room temperature for 10-90days; at 40 ℃ for 10-60 days, the it retained its the bioactivity (+++),which, however, slightly decreased by 90 days (++); its bioactivity was preserved (+++) at 40 ℃ with saturated humidity for 10 days (+++), slightly decreased at 30-60 days (++) and noticeably lowered (+) at 90 days. When preserved for 0, 0.5, 1, 2, and 3 hours in rat seum, the NGF preparation retained stable bioactivity (++++ or +++), which slightly decreased at 4 hours and 6 hours (++).

CONCLUSION:

Liposome-encapsulated NGF has stable bioactivity but its preservation at relatively high temperature with high humidity is difficult.Lyophilized liposome-encapsulated NGF exhibits better bioactivity than NGF-liposome suspension after preservation under various conditions.