Immune biomarker response depends on choice of experimental pain stimulus in healthy adults: a preliminary study

Menstrual cycle-related changes in HPA axis reactivity to acute psychosocial and physiological stressors - a systematic review and meta-analysis of longitudinal studies

Sex disparities are evident in the biological response to acute stressors, with a suggested influence of ovarian hormones on hypothalamic-pituitary-adrenal (HPA) axis functioning. This systematic review and meta-analysis investigates differences in HPA axis reactivity to acute psychosocial or physiological stressors between menstrual cycle phases. A systematic literature search of six databases resulted in 12 longitudinal studies (n = 182) examining HPA axis reactivity in healthy, naturally-cycling, non-breastfeeding participants aged between 18 and 45 years in at least two cycle phases. The quality of cortisol and menstrual cycle assessment was rated and a descriptive synthesis and meta-analysis of HPA axis reactivity between two broader and five more precise cycle phases was conducted. Three studies provided sufficient data for the meta-analysis and showed a significant, small-sized effect, indicating higher cortisol reactivity in the luteal than in the follicular cycle phase. More primary studies with high-quality menstrual cycle and cortisol assessment are needed. The review did not receive funding and was pre-registered (PROSPERO; CRD42020181632).

Association between systemic inflammation and experimental pain sensitivity in subjects with pain and painless neuropathy after traumatic nerve injuries

OBJECTIVES

Peripheral neuropathies that occur secondary to nerve injuries may be painful or painless, and including a low-grade inflammation and pro-inflammatory cytokines associated with both regeneration and damage of peripheral nerve cells and fibers. Currently, there are no validated methods that can distinguished between neuropathic pain and painless neuropathy. The aim of this study was to search for proinflammatory and anti-inflammatory proteins associated with pain and experimental pain sensitivity in subjects with surgeon-verified nerve injuries in the upper extremities.

METHODS

One hundred and thirty-one subjects [69 with neuropathic pain, NP; 62 with painless neuropathy, nP] underwent a conditioned pain modulation (CPM) test that included a cold pressor task (CPT) conducted with the non-injured hand submerged in cold water (4 °C) until pain was intolerable. CPM was assessed by pain ratings to pressure stimuli before and after applying the CPT. Efficient CPM effect was defined as the ability of the individual's CS to inhibit at least 29% of pain (eCPM). The subjects were assigned to one of two subgroups: pain sensitive (PS) and pain tolerant (PT) after the time they could tolerate their hand in cold water (PS<40 s and PT=60 s) . Plasma samples were analyzed for 92 proteins incorporated in the inflammation panel using multiplex Protein Extension Array Technology (PEA). Differentially expressed proteins were investigated using both univariate and multivariate analysis (principal component analysis-PCA and orthogonal partial least-squares discriminant analysis-OPLS-DA).

RESULTS

Significant differences in all protein levels were found between PS and PT subgroups (CV-ANOVA p<0.001), but not between NP and nP groups (p=0.09) or between inefficient CPM (iCPM) and eCPM (p=0.53) subgroups. Several top proteins associated with NP could be detected using multivariate regression analysis such as stromelysin 2 (MMPs), interleukin-2 receptor subunit beta (IL2RB), chemokine (C-X-C motif) ligand 3 (CXCL3), fibroblast growth factor 5 (FGF5), chemokine (C-C motif) ligand 28 (CCL28), CCL25, CCL11, hepatocyte growth factor (HGF), interleukin 4 (IL4), IL13. After adjusting for multiple testing, none of these proteins correlated significantly with pain. Higher levels of CCL20 (p=0.049) and CUB domain-containing protein (CDCP-1; p=0.047) were found to correlate significantly with cold pain sensitivity. CDCP-1 was highly associated with both PS and iCPM (p=0.042).

CONCLUSIONS

No significant alterations in systemic proteins were found comparing subjects with neuropathic pain and painless neuropathy. An expression of predominant proinflammatory proteins was associated with experimental cold pain sensitivity in both subjects with pain and painless neuropathy. One these proteins, CDC-1 acted as "molecular fingerprint" overlapping both CPM and CPT. This observation might have implications for the study of pain in general and should be addressed in more detail in future experiments.

Individuals with both higher recent negative affect and physical pain have higher levels of C-reactive protein

Conceptualizing physical pain and negative affect as potentially interactive, we hypothesized that higher levels of peripheral inflammatory markers would be observed consistently only among individuals with both higher negative affect and pain symptomatology. Participants were generally healthy midlife adults from the Bronx, NY (N ​= ​212, M_age ​= ​46.77; 60.8% Black, 25.5% Hispanic/Latina/o) recruited as part of a larger study. Key measures were: reported pain intensity and pain interference at baseline, recent negative affect averaged from self-reports 5x/day for 7 days, and peripheral inflammatory markers (C-reactive protein [CRP] and a composite cytokine measure based on seven cytokines). Controlling for age, BMI, gender, and education, recent negative affect significantly interacted with both pain variables to explain variance in CRP, with higher CRP levels observed only in individuals with both higher negative affect and either higher pain intensity or pain interference. These findings contribute to an emerging literature suggesting that negative affect, pain, and inflammation are related in important and complex ways.

The interaction between stress and chronic pain through the lens of threat learning

Stress and pain are interleaved at multiple levels - interacting and influencing each other. Both are modulated by psychosocial factors including fears, beliefs, and goals, and are served by overlapping neural substrates. One major contributing factor in the development and maintenance of chronic pain is threat learning, with pain as an emotionally-salient threat - or stressor. Here, we argue that threat learning is a central mechanism and contributor, mediating the relationship between stress and chronic pain. We review the state of the art on (mal)adaptive learning in chronic pain, and on effects of stress and particularly cortisol on learning. We then provide a theoretical integration of how stress may affect chronic pain through its effect on threat learning. Prolonged stress, as may be experienced by patients with chronic pain, and its resulting changes in key brain networks modulating stress responses and threat learning, may further exacerbate these impairing effects on threat learning. We provide testable hypotheses and suggestions for how this integration may guide future research and clinical approaches in chronic pain.

Age differences in salivary markers of inflammation in response to experimental pain: does venipuncture matter?

An important consideration in mechanistic research using biomarkers should include the use of saliva as an alternative to blood. The use of saliva would allow the study of susceptible populations such as older adults where venipuncture may not be feasible. Although saliva has been most commonly used to measure cortisol and tumor necrosis factor-α (TNFα), there is limited evidence that other cytokines found in saliva significantly change in response to laboratory-induced pain. Therefore, the aim of the current preliminary study was to characterize the time course, duration and magnitude of changes of commonly measured pro- (interleukin [IL]-6, IL-8) and anti-inflammatory (IL-10, IL-4) cytokines in saliva samples and to test for age-related differences in separate experimental painful and non-painful control sessions. In addition, we also tested whether venipuncture results in significant cytokine alterations similar to a painful stimulus in a non-painful, non-venipuncture control session. All cytokines were significantly induced by the cold pressor task compared to a warm control session (p < 0.001). Specifically, healthy older adults experienced greater salivary changes in all cytokines during the cold pressor session compared to younger adults in the non-painful sessions (p < 0.001). There were no significant differences between the venipuncture and non-venipuncture sessions across all cytokines (p > 0.05). Our findings support the use of saliva as a substitute for blood in both young and older healthy individuals to measure changes after experimental pain stimulation. In addition, venipuncture alone is not sufficient to induce IL-6, IL-8, IL-10 and IL-4. Future studies in the community are urgently needed to validate and further move translational mechanistic pain research to those populations most underrepresented in clinical research.

Investigating the Burden of Chronic Pain: An Inflammatory and Metabolic Composite

Background. Chronic pain is associated with increased morbidity and mortality, predominated by cardiovascular disease and cancer. Investigating related risk factor measures may elucidate the biological burden of chronic pain. Objectives. We hypothesized that chronic pain severity would be positively associated with the risk factor composite. Methods. Data from 12,982 participants in the 6th Tromsø study were analyzed. Questionnaires included demographics, health behaviors, medical comorbidities, and chronic pain symptoms. The risk factor composite was comprised of body mass index, fibrinogen, C-reactive protein, and triglycerides. Chronic pain severity was characterized by frequency, intensity, time/duration, and total number of pain sites. Results. Individuals with chronic pain had a greater risk factor composite than individuals without chronic pain controlling for covariates and after excluding inflammation-related health conditions (p < 0.001). A significant "dose-response" relationship was demonstrated with pain severity (p < 0.001). In individuals with chronic pain, the risk factor composite varied by health behavior, exercise, lower levels and smoking, and higher levels. Discussion. The risk factor composite was higher in individuals with chronic pain, greater with increasing pain severity, and influenced by health behaviors. Conclusions. Identification of a biological composite sensitive to pain severity and adaptive/maladaptive behaviors would have significant clinical and research utility.

Opioid treatment of experimental pain activates nuclear factor-κB

OBJECTIVE

To determine the independent and combined effects of pain and opioids on the activation of an early marker of inflammation, nuclear factor-κB (NF-κB).

DESIGN

NF-κB activation was compared within-subjects following four randomly ordered experimental sessions of opioid-only (intravenous fentanyl 1 μg/kg), painonly (cold-pressor), opioid + pain, and a resting condition.

SETTING

University General Clinical Research Center.

PARTICIPANTS

Twenty-one (11 female) healthy controls.

INTERVENTIONS

Following exposure to treatment (fentanyl administration and/or cold-pressor pain), blood samples for NF-κB analysis were obtained.

MAIN OUTCOME MEASURES

Intracellular levels of activated NF-κB, in unstimulated and stimulated peripheral blood mononuclear cells at 15 and 30 minutes.

RESULTS

Neither pain nor opioid administration alone effected NF-κB levels in cell populations; however, the combination of treatments induced significant increases of NF-κB in stimulated peripheral blood mononuclear cell, lymphocytes, and monocytes.

CONCLUSIONS

The combination of acute pain with opioids, as occurs in clinical situations, activates a key transcription factor involved in proinflammatory responses.