Human Studies

We have reported child anxiety sensitivity (CASI) predicts chronic post-surgical pain (CPSP). Here, we evaluated DNA methylation profiles to understand gene-environmental interactions underlying CPSP and CASI, in order to identify shared, enriched, genomic pathways. In 73 prospectively recruited adolescents undergoing spine fusion, preoperative CASI, and pain data over 12 months post-surgery were collected. DNA from peripheral blood of evaluable subjects with (n=16) and without CPSP (n=40) were analyzed using MethylationEPIC arrays. We identified 637 and 2,445 differentially methylated positions (DMPs) associated with CPSP and CASI respectively (p≤0.05). Ingenuity pathway analysis of 39 genes with DMPs for both CPSP and CASI revealed enrichment of several canonical pathways, including GABA receptor (p=0.00016 (CPSP); 0.0008 (CASI)) and Dopamine-DARPP32 Feedback in cAMP (p=0.004 (CPSP) and 0.00003 (CASI)) Signaling. Gene-gene interaction network enrichment analysis revealed participation of pathways in cell signaling, molecular transport, metabolism and neurological diseases (p-value <10-8). Bioinformatic approaches to identify histone marks and transcription factor (TF) binding events underlying DMPs, showed their location in active regulatory regions in pain pathway relevant brain cells. Using Enrichr/Pinet enrichment and Library of Integrated Network-Based Cellular Signatures (LINCS) knockdown signatures, we identified TFs regulating genes with DMPs in association with CPSP and CASI. In conclusion, we identified epigenetically enriched pathways associated with CPSP and anxiety sensitivity in children undergoing surgery. Our findings support GABA hypofunction and Dopamine-DARPP32 pathway's roles in emotion/reward and pain. This pilot study provides new epigenetic insights into the pathophysiology of CPSP, and a basis for future studies in biomarker development and targetable interventions. Perspective: Differential DNA methylation in regulatory genomic regions enriching shared neural pathways were associated with chronic post-surgical pain and anxiety sensitivity in adolescents undergoing spine surgery. Our findings support GABA hypofunction and Dopamine-DARPP32 pathway's roles in emotion/reward contributing to behavioral maintenance of pain 10-12 months after surgery.

To explore the role of strong negative emotions in spinal nociception, we evaluated the effect of fear-relevant videos of small animals on the nociceptive withdrawal reflex (NWR) and reflex-related pain perception in healthy subjects with a specific phobia of small animals. Twenty healthy subjects with a specific phobia of small animals diagnosed according to DSM-V criteria were included in this study. The NWR was evoked in the lower limb by stimulating the sural nerve and recording EMG activity in the biceps femoris. NWR pain-related perception was quantified on an 11-point numerical rating scale (NRS). Subjects were examined during 4 recording sessions. In the baseline session, no images were projected. In the other sessions, the subjects were invited to watch a video containing either neutral or phobic content. To evaluate neurovegetative responses, we measured heart rate using a pulse oximeter during each recording session. A series of clinical rating scales were administered to subjects to evaluate disgust, fear, and anxiety. The NWR amplitude was significantly increased during the phobic video session and was associated with the fear inventory scale scores. Women showed higher NWR amplitude values during the phobic video session and a lower recovery rate during the after-effect video session than did men. The NWR amplitude and related pain perception were dissociated from each other during the phobic video session, as the NRS score remained unchanged while the NWR increased in amplitude. Emotions induced by the viewing of phobic videos seem to enhance the activation of the spinal circuitries involved in nociception and the withdrawal reaction without interfering with pain processing pathways or dissociating the reflex response from related pain perception. This effect appears to differ by sex, as it was more intense and longer lasting in women than in men. Emotions induced by phobic video viewing increase the alertness devoted to the defensive reaction by emphasizing nociceptive responses independently from pain perception. The NWR may represent an interesting tool for exploring the interaction between strong negative emotions and spinal nociception. A better understanding of this mechanism may be a theoretical prerequisite for the optimization of pain management in several chronic pain syndromes.

Previous studies have shown a robust correlation between variability of clinical pain scores and responsiveness to placebo (but not active drug) in pain studies, but explanations for these relationships are lacking. We investigated this further by assessing relationship between the Focused Analgesia Selection Test (FAST); a psychophysical method that quantifies pain reporting variability in response to experimental stimuli, variability of daily clinical pain scores as captured via diary, and response to treatment in the context of a randomized controlled crossover trial of naproxen vs. placebo in knee osteoarthritis. Evoked pain using the Staircase-Evoked Pain Procedure (StEPP®) served as the primary efficacy endpoint. Variability of daily pain scores and the FAST were assessed at baseline. Fifty-five subjects completed the study and were included in the analyses. Our results indicated a statistically significant, moderate linear relationship between variability of clinical and experimental pain reports (r= -0.416, P=0.004); and both also correlated with the placebo response (r= 0.393, P=0.004; r=-0.371, P=0.009 respectively), but only the FAST predicted the treatment difference between naproxen and placebo, as demonstrated both in a regression model (P=0.002, Beta=0.456, t=3.342) and in a Receiver Operator Curve analysis (ROC=0.721). Our results extend previous findings to include a correlation between experimental pain variability and the placebo response, and suggest that experimental pain variability is a better predictor of patients who respond preferentially to drug over placebo. A theoretical model unifying these observations is proposed and practical implications are discussed.

Sleep disturbance and chronic pain are related. The present study evaluated both direct and indirect (mediated) pathways through which sleep disturbance might be related to chronic pain intensity and function.