Investigation of the relationship between pain intensity and neuroinflammatory neuropeptides in patients with lumbar disc herniation

Objective: In our study, we compared the serum levels of vasoactive sensory neuropeptides Calcitonin Gene-Related Peptides (CGRP), Substance P (SP) and Vasoactive İntestinal Polypeptide (VIP), Pituitary Adenylate Cyclase Activating Polypeptide 38 (PACAP38) in blood taken before and after microdiscectomy operation in patients with single level lumbar disc herniation (LDH) and radicular pain levels questioned with simultaneous visual analog scale (VAS). We planned to examine those neuropeptides associated with LDH-Induced radicular pain. Materials and Methods: Thirty patients with sciatica, aged between 18-70 years, who were admitted to B.A.İ.B.Ü Medical Faculty Hospital, Department of Neurosurgery, diagnosed with single level lumbar disc herniation by lumbar MRI and planned for microsurgery, and who had not undergone any previous operation in the lumbar region were included in the study group. The control group included 30 healthy individuals who did not have pain in any region, did not use analgesic anti-inflammatory drugs, did not have known lumbar disc herniation, any chronic neuroinflammatory disease and allergic disease. Age, existing chronic diseases, smoking, alcohol consumption and occupational groups were also questioned by scoring the pain of the selected patient and control groups. Approximately 12 cc of blood was taken from each group. The severity of radicular pain of patients just before blood collection was determined with a numerical value between 0 and 10 using the Visual Analogue Scale. All the collected blood was placed in purple capped hemogram tubes in tubes containing EDTA and Protease. After centrifugation, SP, CGRP, VIP and PACAP38 vasoactive neuroinflammatory markers were stored at -20oC until measurement by ELISA. Immunoreactive neuropeptide contents of the samples were used for the measurement of neuropeptide (SP, CGRP, VIP and PACAP38) concentrations in the collected plasma samples. Assay protocol was applied according to the manufacturer's instructions. Findings: Plasma CGRP, SP, VIP and PACAP38 levels of pre-operative patients were found to be significantly increased compared to the control group (p< 0.001, Mann-Whitney U test). On the other hand, plasma CGRP, SP and VIP levels of the same patients were found to be significantly decreased in the post-operative period compared to their pre-operative periods (p< 0.001, Wilcoxon signed-rank test). Plasma PACAP38 level in the post-operative period was found to be significantly increased compared to the plasma level in the preoperative period (p< 0.001, Wilcoxon signed-row test). It was determined that there was no significant correlation between the mean VAS pain socket values of the preoperative and postoperative patients and the plasma CGRP, SP, PACAP-38 and VIP values. (p>0.05). Results: In our study, we showed that CGRP, SP and VIP, whose plasma levels increase in the preoperative period and decrease in the postoperative period, play an important role in the neuroinflammation caused by nerve root compression in LDH and in the pathophysiology of radicular pain, and also we showed that they can be biomarker candidates that can be used in diagnosis and follow-up as they are easily measurable.