Effect on peripheral nerve regeneration by transgenein vivowith human insulin-like growth factor-1

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Abstract

BACKGROUND:

Human insulin-like growth factor (hIGF-1) has been successful in treating peripheral nerve injury, but it is still unclear whether hIGF-1 after transgene in vivo has the effect on promoting the regeneration of peripheral nerve.

OBJECTIVE:

To observe the effect of hIGF-1 on the regeneration of peripheral nerve by transgene in vivo with electrophysiology, histological morphology and ultromicro morphology.

DESIGN:

A univariate design.

SETTINGS:

Jilin Institute of Surgery, China-Japan Friendship Hospital Affiliated to Jilin University; School of Basic Medical Sciences, Jilin University.

MATERIALS:

Thirty male adult Wistar rats of grade II, weighing 200–250 g, were provided by the Animal Experimental Center of Jilin University [certification number: SCXK-(Ji)20030001]. The rats were raised in the environment at the temperature of 25 °C and humidity of 70%. All the rats were randomly divided into hIGF-1-treated group, treatment control group and blank control group, 10 rats in each group. Positive liposomes (mass concentration of 2 g/L) and pcDNA3.1 (mass concentration of 1 g/L) were purchased from Beijing Yuanpinghao Company; pcDNAhIGF-1 (mass concentration of 1 g/L) was provided by Dr. Shen from the School of Public Health of Jilin University. The liposomes were mixed with plasmids with the mass ratio of 1.5 to 10. Operative microscope was made by Jiangsu Zhenjiang Microsurgical Instrument Factory; EMB-5304K electromyogram (EMG) evoked potential meter by Nihon Kohden Corporation. HPIAS-1 000 high-acuity color pathological imaging analytical system (Japan) and JEM-1200EX transmission electron microscope (Japan) were also used.

METHODS:

The experiments were carried out in Jilin Institute of Surgery from April to June in 2004. ① All the rats were anesthetized, and the right sciatic nerve was exposed, and it was clipped with a clip at 5 mm below the piriform muscle for 3 times, 10 s for each time. The pressed width was 3 mm, and formed as membrane under operating microscope (×6). Rats in the hIGF-1-treated group were subepineurially injected with the mixture of pcDNAhIGF-1 and positive liposomes (10 μL) immediately, those in the treatment control group were injected with the mixture of pcDNA3.1, positive liposomes and distilled water (10 μL), and those in the blank control group were not given any injection. ② The sciatic nerve functional indexes (SFI) were measured within 56 days postoperatively according to the methods used by Shen et al. ISFI=0 was taken as normal, and ISFI=−100 as completely damaged. EMG evoked potential meter was used to record the electrophysiological changes of the regenerated nerve fibers. The indexes of histological morphology in 5 randomly selected sights were determined with the color pathological imaging analytical system, and the ultrostructures of the regenerated nerve fibers were also observed.

MAIN OUTCOME MEASURES:

① Comparison of the SFI within 56 days postoperatively; ② Comparison of the electrophysiology, histological morphology and ultrastructure of the regenerated nerve fibers 56 days postoperatively. RESULTS: All the 30 Wistar rats were involved in the analysis of results. ① SFI: The SFI values were gradually increased as time prolonged in all the three groups, and the changes were more obvious after 24 days, the SFI values recovered better at each time point in the hIGF-1-treated group than in the other two groups. ② Eelectrophysiological results of right sciatic nerve: The latency of motor evoked potential (MEP) was close between the treatment control group and the blank control group [(2.55±0.36), (2.65±0.55) ms, P > 0.05], but higher in the hIGF-1-treated group [(2.14±0.22) ms] than in the blank control group (P < 0.01). The amplitude and conduction velocity of MEP in the treatment control group [(6.67±0.69) mV, (29.57±4.06) m/s] were close to those in the blank control group [(6.60±0.59) mV, (29.22±3.20) m/s, P> 0.05], but those in the hIGF-1-treated group [(7.81±0.84) mV, (36.91± 4.37) m/s] were larger or faster than those in the blank control group (P< 0.01). ③ Results of the pathological image analysis of the regenerated nerve fibers: The axonal diameter, thickness of myelin sheath of the regenerated nerve fiber and the number of myelinated nerve fiber in the treatment control group [(2.28±0.33) μm, (1.08±0.18) μm2, (71.80±8.25) fibers] were close to those in the blank control group [(2.18±0.29) μm, (1.03±0.15) μm2, (68.60± 8.55) fibers] (P > 0.05), and those in the hIGF-1-treated group [(3.03±0.35) μm, (1.65±0.24) μm2, (88.20±8.82) fibers] were obviously larger or more than those in the blank control group (P < 0.01). ④ Ultrastructure of the regenerated nerve fibers of sciatic nerve: In the hIGF-1-treated group, the regenerated fibers of sciatic nerve were more and mature, manifested by thicker nerve fibers, thicker and evener myelin sheath, which were better than those in the other two groups.

CONCLUSION:

The results of the quantitative parameters of the electrophysiology, gross histological morphology and ultrostructural changes in the process of repairing damaged peripheral nerve indicate that transgene in vivo with hIGF-1 can promote the neural regeneration after peripheral nerve injury.

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