|Home | About | Journals | Submit | Contact Us | Français|
Inflammatory cytokines secreted from the nucleus pulposus are thought to lead to lumbar nerve root compression-like symptoms. Tumor necrosis factor-alpha (TNF-α), an inflammatory cytokine, likely plays an important role in lumbar disc hernia-related leg pain. In this experimental study, we compared the effectiveness of TNF-α antagonists administered through the intravenous or epidural route in lumbar spine pathologies.
After ethics committee approval had been obtained, 24 Sprague Dawley male rats aged 70–90 days and weighing 250–300 g each were allocated to four groups. In Group I, only the surgical procedure was performed; in Group II, 1 ml of saline solution was administered into the epidural field; in Group III, 10 mg/kg of infliximab was administered into the coccygeal vein; and in Group IV (epidural group), 25 mg of etanercept was administered into the epidural region.
When the left leg pull values were analyzed on day 14, whereas there was not a significant difference among the three groups, a decreasing difference was observed in Group IV (P < 0.05). When the 21st and 28th day left leg pull values were compared between groups, the values from Groups II, III, and IV were significantly lower than those of Group I (P < 0.05).
The absence of a difference between the baseline values and left leg pull values on days 14, 21, and 28 in Group IV indicates that recovery began on day 21 with the epidural administration of etanercept. There was no difference between intravenous saline administration and intravenous infliximab administration with regard to the start of the recovery. In the present study of rats with discopathy, TNF-α antagonists administered epidurally led to earlier recovery from radiculopathy-related allodynia compared to intravenous administration.
Lumbar disc hernia is the most common cause of radicular pain. Many scientific studies in recent years have attempted to elucidate the pathophysiologic mechanism of lumbar disc hernia-related pain. Inflammatory cytokines secreted from the nucleus pulposus may lead to lumbar nerve root compression-like symptoms.[1,2] Animal studies have shown that application of the nucleus pulposus to the epidural field disrupts regional blood flow and causes morphologic and functional changes in the neural structure, even in the absence of nerve root compression.[3,4] Inflammatory cytokines such as interleukin (IL)-1 and IL-6 are secreted from cells in the nucleus pulposus. Tumor necrosis factor-alpha (TNF-α), an inflammatory cytokine, is also present in the nucleus pulposus. It is not clear but TNF-α may play an important role in lumbar disc hernia-related leg pain. Various methods for the administration of exogenous TNF-α to nerve roots have been examined in animal studies, focusing on the effects of each method on pain-related behaviors. Chronic low back pain and radicular pain is still an unresolved problem despite many studies. Every year, many patients undergo surgery due to spinal stenosis or disc hernia-related radiculopathy and pain. The expected postoperative benefit may not always be obtained, and pain may continue beside treatment costs and loss of labor. Patient satisfaction decreases while operative complications increase. Restriction of daily living activities due to chronic pain is a burden to both patients and health staff. Patients with lower back pain should be treated with conservative and minimally invasive procedures such as pharmacological methods and physical therapy before planning surgical treatment. The most commonly performed minimally invasive procedure is lumbar epidural steroid administration.[8,9] This method has some limitations, although good outcomes may be obtained with proper patient selection. The goal of this study was to identify intravenous agents that could take the place of the pharmacologic agents applied in the epidural field.
Although monoclonal anti-TNF-α antibodies are widely used to treat inflammatory joint diseases such as rheumatoid arthritis and ankylosing spondylitis,[10,11] few data are available on the effects of monoclonal anti-TNF-α antibodies in lumbar spinal pathologies.[12,13] Therefore, this experimental study investigated the effectiveness of TNF-α antagonists administered through the intravenous or epidural route in lumbar disc pathologies.
This study was conducted with 24 Sprague Dawley male rats aged 70–90 days and weighing 250–300 g each, following ethics committee approval from Abant Izzet Baysal University's animal testing laboratory (date: 15.04.2014; number: B.30.2.ABÜ.0.05.05–050.01.04–119). The rats were kept under a regular photoperiod (12 h of light and 12 h of darkness) at normal room temperature (295.15 K), and were given standard pellet rat chow (210 kcal/100 g/day) and tap water. Sacrifice was performed by cervical dislocation under general anesthesia after the study.
All surgical procedures were performed under general anesthesia provided with 50 mg/kg of intraperitoneal ketalar (Ketamine-HCl; Pfizer, New York City, NY, USA). The depth of anesthesia was evaluated with skin pinching responses.
All surgical procedures were performed by the same surgeon using standard techniques with the rats placed into proper positions on special fixation boards. The rats were randomly allocated to four groups through the sealed envelope method. The experimental lumbar discopathy model was applied as described by Sasaki et al. In all groups, the lumbar region was opened through a midline incision, and the para-spinal muscles were separated from the L5–L6 lamina under an operation microscope. A laminectomy pocket was made at 2.5 mm without shredding the L5–L6 facet joint in an L5 spinal arc using a drill (diameter: 1 mm). The left L5 nerve root and dorsal root ganglion were exposed through an L5 partial lamina pocket [Figure 1a]. Pre- or post-operative antibiotic prophylaxis was not used.
Group I (n = 6): The surgical procedure was performed and the spinal muscles were sutured, after which the skin was closed with metal clips.
Group II (n = 6): The lumbar region was surgically opened as defined in Group I. The nucleus pulposus was prepared from the coccygeal vertebral disc and placed at the beginning of the dorsal root ganglion through the laminectomy pocket and a discopathy was created. Afterward, 1 ml of saline solution was administered into the epidural region.
Group III (n = 6): The lumbar region was surgically opened as defined in Group I. The nucleus pulposus was prepared from the coccygeal vertebral disc and placed at the beginning of the dorsal root ganglion through the laminectomy pocket and a discopathy was created. Afterward, 10 mg/kg of infliximab (Remicade® 100 mg vial; Schering-Plough, Kenilworth, NJ, USA) was administered into the coccygeal vein.
Group IV (n = 6): The lumbar region was surgically opened as defined in Group I. The nucleus pulposus [Figure 1b] was prepared from the coccygeal vertebral disc and placed at the beginning of the dorsal root ganglion through the laminectomy pocket and a discopathy was created. Afterward, 25 mg of etanercept (Enbrel® 25 mg vial; Pfizer) were administered epidurally.
Tactile allodynia was evaluated through the Von Frey test by a person blinded to the study protocol before surgery and on days 7, 14, 21, and 28 following discopathy. For the Von Frey test, rats were placed in a rectangular enclosure with a wire floor surrounded by glass equal pressure was applied to the rats’ feet with Von Frey filaments (Touch Test® Sensory Evaluator; North Coast Medical Inc., Gilroy, CA, USA; Figure 2) of different diameters. The filament diameter values that caused a leg pull or bounce response after pressure (pain factor) were recorded as responses to the mechanical stimulus. Primary outcomes of study are leg pull values of the rat. All data were collected on day 28 of the study after which all subjects were humanely euthanized with cervical dislocation under general anesthesia. All study was performed in 30 days.
Statistical analyses were performed using IBM SPSS version 20.0 (IBM Corp., Armonk, NY, USA) and an ANOVA test was used for inter-group comparisons. Baseline and subsequent assessments within groups were performed with paired sample t-test. The value of P < 0.05 was considered to be statistically significant.
Paralysis was not observed in any rats. In Groups II and III, the left leg pull values measured on days 7 and 14 were lower than the baseline values, whereas the left leg pull values on days 21 and 28 were similar to the baseline values. In Group IV, the left leg pull value on day 7 was significantly lower than the baseline values (P < 0.05). In Group IV, there was no statistically significant difference between the left leg pull values on days 14, 21, and 28 and the baseline values (P > 0.05). There was also no difference between the left leg pull values of all groups at baseline (P > 0.05). Regarding the day 14 values while there was no significant difference between Groups I, and IV. Regarding the left leg pull values on days 21 and 28, the values of Groups II, III, and IV were no significant difference than Group I [P < 0.05, Table 1].
This animal study shows that the epidural administration of TNF-α agonists provided earlier recovery from radiculopathy-related allodynia compared to intravenous administration.
Clinical trials have shown that anti-TNF-α antibodies reduced lumbar disc hernia-related pain.[5,12] Some researchers have reported that the administration of anti-TNF-α antibodies reduced spontaneous behavior and allodynia in rats with experimentally-induced disc injury. Olmarker and Rydevik noticed that infliximab (monoclonal anti-TNF-α antibodies) facilitated nerve conduction when applied to the nucleus pulposus and limited nerve fiber injury, intra-capillary thrombus formation, and intra-neural formation in experimental Metin disc injury models. However, the effects of each mode of administration of TNF-α are not known. In Groups II, III, and IV, the left leg pull responses measured on postoperative day 7 developing with thinner von Frey filaments compared to the baseline values were interpreted as artificial discopathy-related allodynia. All other measurements in Group I were similar to the baseline values. Although the left leg pull values measured on days 7 and 14 were lower than the baseline values in Groups II and III, the left leg pull values measured on days 21 and 28 were similar to the baseline values; this was evaluated as recovery starting from day 21, and there was no difference between intravenous saline administration and intravenous infliximab administration with regard to the start of recovery. The lack of a difference between the baseline values and left leg pull values on days 14, 21, and 28 in Group IV indicates that epidural etanercept administration led to recovery from discopathy-related allodynia earlier compared to intravenous infliximab administration. Sasaki et al. used an experimental lumbar disc hernia model involving the application of the nucleus pulposus into the epidural field and found that TNF-α antagonists reduced allodynia when administered just after surgery or 6 months later. We applied a single dose of a TNF-α antagonist just after surgery and detected that allodynia ended earlier when etanercept was administered in the epidural field. Olmarker et al. reported that a single dose of infliximab prevented pain-related behavior changes and the development of allodynia in the hind leg for a couple of weeks in lumbar disc hernia rat models. In this study, the rats were evaluated for 4 weeks, and TNF-α antagonists administered through the epidural route prevented allodynia for up to 4 weeks following recovery. Sommer et al. showed that local or systemic etanercept reduced pain-related behavior changes in rats with experimentally-induced neuropathy. Although the results of our study are consistent with those of Sommer et al., we found that the epidural administration of TNF-α antagonists promoted earlier recovery compared to systemic administration.
Infliximab and etanercept have different properties. Infliximab can neutralize all forms such as extracellular, transmembrane, and receptor-bound TNF-α. Due to the modified form of Etanercept, it is not possible to neutralize the receptor-bound TNF-α. Infliximab and etanercept have different elimination half-lives (115 and 210, respectively). The most important limitation of the study is ignoring diferent elimination half-lives.
This experimental study shows that the epidural administration of TNF-α antagonists provided earlier recovery from radiculopathy-related allodynia compared to intravenous administration in rats with experimentally-induced lumbar discopathy.
This project supported by Sakarya University with project number 2013-08-06-014.
There are no conflicts of interest.