[Nociceptive system : Nociceptors, fiber types, spinal pathways, and projection areas]

Elevated serum TLR4 level as a potential marker for postsurgical chronic pain in pediatric patients with different approaches to analgesia

Introduction

The perioperative period of any surgery is accompanied by immune suppression. The level of Toll-like receptor 4 (TLR4) is known to increase in inflammation and after nerve injury and contributes to the development of neuropathic pain. The interaction of TLRs in response to the effect of opioids results in paradoxical hyperalgesia. Regional anesthesia techniques are the standard of care for perioperative pain management in children.

Aim

The aim of the study was to determine and evaluate the indicators of TLR4 for different methods of pain relief in anesthetic management of hernia repair in children and their effect on pain chronification.

Materials and methods

There were examined 60 children with inguinal hernia during 2020-2022. Children were divided into 3 groups: Group I included 20 children who underwent surgery under general anesthesia using the block of the anterior abdominal wall-transversalis fascia plane block (TFPB), combined with the quadratus lumborum block (QLB-4) via a single intramuscular injection; Group II included 20 children who underwent surgery under general anesthesia using the TFPB; Group III comprised 20 children who underwent surgery under general anesthesia using opioid analgesics. The levels of TLR4 were evaluated at a discharge from the hospital, 3 and 6 months after surgery.

Results

There was no difference in age and body weight among all groups. In Group II, boys prevailed. In Group III, the length of hospital stay was the longest (3.28 ± 0.24 days, p < 0.05, t = 4.09) as compared to children of Group II and Group I (3.0 ± 0.30 (p < 0.05, t = 2.647) and 2.1 ± 0.16 days, respectively). While staying in the surgical department, children of Group III demonstrated significantly higher FLACC and VAS scores. The prevalence of chronic pain was the highest among children of Group III (35%) as compared to those in Group II and Group I (20 and 15%, respectively). The highest increase in the level of TLR4 was found in the group of opioid analgesia on the third and sixth months after surgery (68.86 + 10.31 pg/ml and 143.15 + 18.77 pg/ml (p < 0.05, t = 6.33), respectively) as compared to patients who received regional anesthesia.

Conclusions

There were confirmed the following advantages of the transversalis fascia plane block combined with the quadratus lumborum block (QLB + TFPB) via a single intramuscular injection: ease of use; adequate perioperative pain control as evidenced by the FLACC and VAS pain assessment scales; reduced perioperative use of opioid analgesics; shortening the length of hospital stay.

Stress and Pain. Predictive (Neuro)Pattern Identification for Chronic Back Pain: A Longitudinal Observational Study

Introduction

Low back pain (LBP) leads to considerable impairment of quality of life worldwide and is often accompanied by psychosomatic symptoms.

Objectives

First, to assess the association between stress and chronic low back pain (CLBP) and its simultaneous appearance with fatigue and depression as a symptom triad. Second, to identify the most predictive stress-related pattern set for CLBP for a 1-year diagnosis.

Methods

In a 1-year observational study with four measurement points, a total of 140 volunteers (aged 18–45 years with intermittent pain) were recruited. The primary outcomes were pain [characteristic pain intensity (CPI), subjective pain disability (DISS)], fatigue, and depressive mood. Stress was assessed as chronic stress, perceived stress, effort reward imbalance, life events, and physiological markers [allostatic load index (ALI), hair cortisol concentration (HCC)]. Multiple linear regression models and selection procedures for model shrinkage and variable selection (least absolute shrinkage and selection operator) were applied. Prediction accuracy was calculated by root mean squared error (RMSE) and receiver-operating characteristic curves.

Results

There were 110 participants completed the baseline assessments (28.2 ± 7.5 years, 38.1% female), including HCC, and a further of 46 participants agreed to ALI laboratory measurements. Different stress types were associated with LBP, CLBP, fatigue, and depressive mood and its joint occurrence as a symptom triad at baseline; mainly social-related stress types were of relevance. Work-related stress, such as “excessive demands at work”[b = 0.51 (95%CI -0.23, 1.25), p = 0.18] played a role for upcoming chronic pain disability. “Social overload” [b = 0.45 (95%CI -0.06, 0.96), p = 0.080] and “over-commitment at work” [b = 0.28 (95%CI -0.39, 0.95), p = 0.42] were associated with an upcoming depressive mood within 1-year. Finally, seven psychometric (CPI: RMSE = 12.63; DISS: RMSE = 9.81) and five biomarkers (CPI: RMSE = 12.21; DISS: RMSE = 8.94) could be derived as the most predictive pattern set for a 1-year prediction of CLBP. The biomarker set showed an apparent area under the curve of 0.88 for CPI and 0.99 for DISS.

Conclusion

Stress disrupts allostasis and favors the development of chronic pain, fatigue, and depression and the emergence of a “hypocortisolemic symptom triad,” whereby the social-related stressors play a significant role. For translational medicine, a predictive pattern set could be derived which enables to diagnose the individuals at higher risk for the upcoming pain disorders and can be used in practice.

Characteristics of sensory neuronal groups in CGRP-cre-ER reporter mice: Comparison to Nav1.8-cre, TRPV1-cre and TRPV1-GFP mouse lines

Peptidergic sensory neurons play a critical role in nociceptive pathways. To precisely define the function and plasticity of sensory neurons in detail, new tools such as transgenic mouse models are needed. We employed electrophysiology and immunohistochemistry to characterize in detail dorsal root ganglion (DRG) neurons expressing an inducible CGRP^cre-ER (CGRP-cre⁺); and compared them to DRG neurons expressing Nav1.8^cre (Nav1.8-cre⁺), TRPV1^cre (TRPV1-cre⁺) and TRPV1-GFP (V1-GFP⁺). Tamoxifen effectively induced CGRP^cre-ER production in DRG. ≈87% of CGRP^cre-ER-expressing neurons were co-labeled CGRP antibody. Three small and two medium-large-sized (5HT3a⁺/NPY2R^- and NPY2R⁺) neuronal groups with unique electrophysiological profiles were CGRP-cre⁺. Nav1.8-cre⁺ neurons were detected in all CGRP-cre⁺ groups, as well as in 5 additional neuronal groups: MrgprD⁺/TRPA1^-, MrgprD⁺/TRPA1⁺, TRPV1⁺/CGRP^-, vGLUT3⁺ and ≈30% of trkC⁺ neurons. Differences between TRPV1^cre and Nav1.8^cre reporters were that unlike TRPV1-cre⁺, Nav1.8-cre⁺ expression was detected in non-nociceptive vGLUT3⁺ and trkC⁺ populations. Many TRPV1-cre⁺ neurons did not respond to capsaicin. In contrast, V1-GFP⁺ neurons were in 4 groups, each of which was capsaicin-sensitive. Finally, none of the analyzed reporter lines showed cre-recombination in trkB⁺, calbindin⁺, 70% of trkC⁺ or parvalbumin⁺ neurons, which together encompassed ≈20% of Nav1.8-cre^- DRG neurons. The data presented here increases our knowledge of peptidergic sensory neuron characteristics, while showing the efficiency and specificity manipulation of peptidergic neurons by the CGRP^cre-ER reporter. We also demonstrate that manipulation of all C- and A-nociceptors is better achieved with TRPV1-cre reporter. Finally, the described approach for detailed characterization of sensory neuronal groups can be applied to a variety of reporter mice.

Pain in the Blood? Envisioning Mechanism-Based Diagnoses and Biomarkers in Clinical Pain Medicine

Chronic pain is highly prevalent, and pain medicine lacks objective biomarkers to guide diagnosis and choice of treatment. The current U.S. “opioid epidemic” is a reminder of the paucity of effective and safe treatment options. Traditional pain diagnoses according to the International Classification of Diseases are often unspecific, and analgesics are often prescribed on a trial-and-error basis. In contrast to this current state of affairs, the vision of future mechanism-based diagnoses of chronic pain conditions is presented in this non-technical paper, focusing on the need for biomarkers and the theoretical complexity of the task. Pain is and will remain a subjective experience, and as such is not objectively measurable. Therefore, the concept of “noci-marker” is presented as an alternative to “pain biomarker”, the goal being to find objective, measurable correlates of the pathophysiological processes involved in different chronic pain conditions. This vision entails a call for more translational pain research in order to bridge the gap between clinical pain medicine and preclinical science.