Korean J Pain.  2012 Oct;25(4):213-220. 10.3344/kjp.2012.25.4.213.

Effects of Ethyl Pyruvate on Allodynia, TNF-alpha Expression, and Apoptosis in the Dorsal Root Ganglion after Spinal Nerve Ligation Injury

• Choi DK
• Leem JG
• Shin JW
• Suh JH

• KMID: 2278161
• DOI: http://doi.org/10.3344/kjp.2012.25.4.213

Abstract

BACKGROUND
It has been demonstrated that the expression of tumor necrosis factor-alpha (TNF-alpha) and apoptotic cell death in the dorsal root ganglion (DRG) following spinal nerve constriction injury play a role in the initiation and continuation of hyperalgesia and allodynia. The present study was designed to investigate the effects of ethyl pyruvate (EP) on mechanical and cold allodynia, TNF-alpha expression, and apoptosis in DRG after spinal nerve ligation injury.
METHODS
Rats were divided into 3 groups: control, pre-EP, and post-EP. EP (50 mg/kg) was intraperitoneally injected 30 minutes before (pre-EP) or after (post-EP) surgery. Behavioral tests to determine mechanical and cold allodynia were conducted before surgery and 4 and 7 days after surgery. Seven days after surgery, TNF-alpha protein levels in DRG were evaluated by enzyme-linked immunosorbent assay, and DRG apoptosis was determined by immunohistochemical detection of activated caspase-3.
RESULTS
Treatment with EP significantly reduced mechanical and cold allodynia following spinal nerve ligation injury. TNF-alpha protein levels in the pre-EP (4.7 +/- 1.2 pg/200 microg; P < 0.001) and post-EP (6.4 +/- 1.8 pg/200 microg; P < 0.001) groups were 2-3 times lower than the control group (14.4 +/- 1.2 pg/200 microg). The percentages of neurons and satellite cells that co-localized with caspase-3 were also significantly lower in the pre-EP and post-EP groups than the control group.
CONCLUSIONS
These results demonstrate that EP has a strong anti-allodynic effect that acts through the inhibition of TNF-alpha expression and apoptosis in DRG after spinal nerve ligation injury.

Keyword

allodynia; apoptosis; dorsal root ganglion; ethyl pyruvate; tumor necrosis factor

MeSH Terms

Animals
Apoptosis
Caspase 3
Cell Death
Cold Temperature
Constriction
Diagnosis-Related Groups
Enzyme-Linked Immunosorbent Assay
Ganglia, Spinal
Hyperalgesia
Ligation
Neurons
Pyruvates
Pyruvic Acid
Rats
Spinal Nerve Roots
Spinal Nerves
Tumor Necrosis Factor-alpha
Caspase 3
Pyruvates
Pyruvic Acid
Tumor Necrosis Factor-alpha

Figure

• 

  Fig. 1 Behavioral tests for (A) mechanical and (B) cold allodynia (n = 21 rats per group). Mechanical allodynia was tested by the application of von Frey filaments to the plantar surface of the hind paw ipsilateral to the spinal nerve ligation injury. Cold allodynia was tested by the application of acetone to the same site. POD, postoperative day. *P < 0.001 compared with the control group.

• 

  Fig. 2 TNF-α expression levels in the dorsal root ganglion (DRG). The TNF-α protein level in the ipsilateral (left) DRGs of the L5/6 spinal segments was measured using ELISA. *P < 0.001 compared with the control group.

• 

  Fig. 3 Activated capsase-3 fluorescence in the dorsal root ganglion (DRG) of the control group. (A) NeuN (green) is a marker of neurons. (D) GFAP (green) is a marker of activated satellite cells. (B, E) Activated caspase-3 (red) is an indicator of apoptosis and was observed by fluorescent staining. Activated caspase-3 was co-localized in (C) DRG neurons and (F) satellite cells. The black arrows indicate where activated caspase-3 is co-localized with NeuN, and the white arrows indicate where activated caspase-3 is colocalized with GFAP. Bar indicates 50 µm. POD, postoperative day.

• 

  Fig. 4 Percentage of neurons and satellite cells that colocalized with caspase-3 in the dorsal root ganglion (n = 7 rats per group). NeuN is a marker of neurons. GFAP is a marker of activated satellite cells. The neurons and satellite cells that co-localized with caspase-3 were counted and are expressed as a percentage of the total neurons or activated satellite cells per section. *P = 0.002 compared with the control group.

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