[Safety of gene therapy within cochlea, experimental study with guinea pig]

To observe the safety of inoculation of recombinant adenovirus with human neurotrophin-3 (Ad-NT3) into cochlea and its effect on hearing function.

Twenty healthy guinea pigs were randomly divided into two groups: ten animals were inoculated with Ad-NT3 into the perilymphatic space after a small hole was drilled in the bony wall near tympanic scala of the base turn, while the other ten were introduced with artificial perilymphatic fluid (APF) as controls. Auditory brainstem response (ABR) were recorded before, immediately after and seven days after the inoculation. Seven days after the surgery, the animals were killed. Frozen sections and colloidin sections of cochlea were made and observed under microscope. Immunohistochemistry was used to detect the expression of NT3 protein in cochlea.

The mean ABR threshold values were (35 +/- 3.7) dB SPL and (35 +/- 3.2) dB SPL before the inoculation, (40 +/- 2.5) dB SPL and (40 +/- 3.0) dB SPL immediately after the inoculation, and (35 +/- 3.0) dB SPL and (35 +/- 3.0) dB SPL seven days after inoculation in the Ad-NT3 group and AFP group respectively (all P > 0.05). The ABR-III latency of 100dB SPL click was (2.812 +/- 0.087) ms and (2.824 +/- 0.121) ms before inoculation, (2.793 +/- 0.093) ms and (2.796 +/- 0.095) ms immediately after inoculation, and (2.822 +/- 0.102) ms and (2.834 +/- 0.135) ms seven days after inoculation in Ad-NT3 and AFP groups respectively (P > 0.05). No difference of ABR threshold and latency was observed at different time points in both groups. Ad-NT3 protein was expressed within each turn of the cochlea, including spiral limbus, spiral ligament and ganglion cells. The cochlear structure remained intact with no sign of infection or cell degeneration.

Gene therapy by means of introduction of trace AdNT3 into the perilymphatic space through pore in tympanic scala is safe, causing no structure change or hearing loss.