The association between selected genetic variants and individual differences in experimental pain.

OBJECTIVES: The underlying mechanisms for individual differences in experimental pain are not fully understood, but genetic susceptibility is hypothesized to explain some of these differences. In the present study we focus on three genetic variants important for modulating experimental pain related to serotonin (SLC6A4 5-HTTLPR/rs25531 A>G), catecholamine (COMT rs4680 Val158Met) and opioid (OPRM1 rs1799971 A118G) signaling. We aimed to investigate associations between each of the selected genetic variants and individual differences in experimental pain. METHODS: In total 356 subjects (232 low back pain patients and 124 healthy volunteers) were genotyped and assessed with tests of heat pain threshold, pressure pain thresholds, heat pain tolerance, conditioned pain modulation (CPM), offset analgesia, temporal summation and secondary hyperalgesia. Low back pain patients and healthy volunteers did not differ in regards to experimental test results or allelic frequencies, and were therefore analyzed as one group. The associations were tested using analysis of variance and the Kruskal-Wallis test. RESULTS: No significant associations were observed between the genetic variants (SLC6A4 5-HTTLPR/rs25531 A>G, COMT rs4680 Val158Met and OPRM1 rs1799971 A118G) and individual differences in experimental pain (heat pain threshold, pressure pain threshold, heat pain tolerance, CPM, offset analgesia, temporal summation and secondary hyperalgesia). CONCLUSIONS: The selected pain-associated genetic variants were not associated with individual differences in experimental pain. Genetic variants well known for playing central roles in pain perception failed to explain individual differences in experimental pain in 356 subjects. The finding is an important contribution to the literature, which often consists of studies with lower sample size and one or few experimental pain assessments.

A genome-wide association study with 1,126,563 individuals identifies new risk loci for Alzheimer's disease.

Late-onset Alzheimer's disease is a prevalent age-related polygenic disease that accounts for 50-70% of dementia cases. Currently, only a fraction of the genetic variants underlying Alzheimer's disease have been identified. Here we show that increased sample sizes allowed identification of seven previously unidentified genetic loci contributing to Alzheimer's disease. This study highlights microglia, immune cells and protein catabolism as relevant to late-onset Alzheimer's disease, while identifying and prioritizing previously unidentified genes of potential interest. We anticipate that these results can be included in larger meta-analyses of Alzheimer's disease to identify further genetic variants that contribute to Alzheimer's pathology.

Predicting the outcome of persistent sciatica using conditioned pain modulation: 1-year results from a prospective cohort study.

Background and aims Recovery in patients hospitalised with severe sciatica is unpredictable. Prognostic tools to aid clinicians in the early identification of patients at risk of developing chronic sciatic pain are warranted. Conditioned pain modulation (CPM) is a psychophysical measure of the endogenous pain modulatory pathways. Several studies have suggested CPM as a potentially important predictive biomarker for the development of chronic pain. The aim of the study was to determine whether CPM effect in patients still suffering from leg pain 6 weeks after hospital discharge for severe sciatica is associated with persistent leg pain at 12 months. A potential association would suggest that measuring CPM effect could be a valuable prognostic tool in the hospital management of sciatica. Methods A prospective cohort study in which CPM effect was measured 6 weeks after hospital discharge following an acute admission with sciatica as the main complaint. The impact of CPM effect on the outcome was analysed using logistic regression. The outcome measured was self-reported leg pain score of ≥1 in the past week on a 0-10 numeric rating scale (NRS) at 12 months post discharge. Results A total of 111 patients completed the entire study, 51 of whom received non-randomised surgical treatment. Crude and confounder adjusted analyses showed no significant association between CPM effect and leg-pain measured at 12 months, crude Odds Ratio 0.87, 95% CI 0.7-1.1, p = 0.23. Conclusions Our results suggest that CPM assessment has limited prognostic value for the long-term outcome in severe sciatica when measured 6 weeks after hospital discharge. Implications The present study adds important knowledge concerning the limited clinical use of late CPM testing in sciatica patients. The heterogeneity in patients, the wide range of treatments received and a generally favourable outcome are factors that may affect CPM's clinical value as a prognostic factor for severe sciatica.

Prognostic Factors for Persistent Leg-Pain in Patients Hospitalized With Acute Sciatica.

STUDY DESIGN: Prospective cohort study. OBJECTIVE: To identify potential prognostic factors for persistent leg-pain at 12 months among patients hospitalized with acute severe sciatica. SUMMARY OF BACKGROUND DATA: The long-term outcome for patients admitted to hospital with sciatica is generally unfavorable. Results concerning prognostic factors for persistent sciatica are limited and conflicting. METHODS: A total of 210 patients acutely admitted to hospital for either surgical or nonsurgical treatment of sciatica were consecutively recruited and received a thorough clinical and radiographic examination in addition to responding to a comprehensive questionnaire. Follow-up assessments were done at 6 weeks, 6 months, and 12 months. Potential prognostic factors were measured at baseline and at 6 weeks. The impact of these factors on leg-pain was analyzed by multiple linear regression modeling. RESULTS: A total of 151 patients completed the entire study, 93 receiving nonrandomized surgical treatment. The final multivariate models showed that the following factors were significantly associated with leg-pain at 12 months: high psychosocial risk according to the Örebro Musculosceletal Pain Questionnaire (unstandardized beta coefficient 1.55, 95% confidence interval [CI] 0.72-2.38, P < 0.001), not receiving surgical treatment (1.11, 95% CI 0.29-1.93, P = 0.01), not actively employed upon admission (1.47, 95% CI 0.63-2.31, P < 0.01), and self-reported leg-pain recorded 6 weeks posthospital admission (0.49, 95% CI 0.34-0.63, P < 0.001). Interaction analysis showed that the Örebro Musculosceletal Pain Questionnaire had significant prognostic value only on the nonsurgically treated patients (3.26, 95% CI 1.89-4.63, P < 0.001). CONCLUSION: The results suggest that a psychosocial screening tool and the implementation of a 6-week postadmission follow-up has prognostic value in the hospital management of severe sciatica. LEVEL OF EVIDENCE: 2.

Antibiotic treatment In patients with chronic low back pain and Modic changes (the AIM study): study protocol for a randomised controlled trial.

BACKGROUND: A previous randomised controlled trial (RCT) of patients with chronic low back pain (LBP) and vertebral bone marrow (Modic) changes (MCs) on magnetic resonance imaging (MRI), reported that a 3-month, high-dose course of antibiotics had a better effect than placebo at 12 months' follow-up. The present study examines the effects of antibiotic treatment in chronic LBP patients with MCs at the level of a lumbar disc herniation, similar to the previous study. It also aims to assess the cost-effectiveness of the treatment, refine the MRI assessment of MCs, and further evaluate the impact of the treatment and the pathogenesis of MCs by studying genetic variability and the gene and protein expression of inflammatory biomarkers. METHODS/DESIGN: A double-blinded RCT is conducted at six hospitals in Norway, comparing orally administered amoxicillin 750 mg, or placebo three times a day, over a period of 100 days in patients with chronic LBP and type I or II MCs at the level of a MRI-confirmed lumbar disc herniation within the preceding 2 years. The inclusion will be stopped when at least 80 patients are included in each of the two MC type groups. In each MC type group, the study is designed to detect (ß = 0.1, α = 0.05) a mean difference of 4 (standard deviation 5) in the Roland Morris Disability Questionnaire score between the two treatment groups (amoxicillin or placebo) at 1-year follow-up. The study includes cost-effectiveness measures. Blood samples are assessed for security measures and for possible inflammatory mediators and biomarkers at different time points. MCs are evaluated on MRI at baseline and after 12 months. A blinded intention-to-treat analysis of treatment effects will be performed in the total sample and in each MC type group. DISCUSSION: To ensure the appropriate use of antibiotic treatment, its effect in chronic LBP patients with MCs should be re-assessed. This study will investigate the effects and cost-effectiveness of amoxicillin in patients with chronic LBP and MCs at the level of a disc herniation. The study may also help to refine imaging and characterise the biomarkers of MCs. TRIAL REGISTRATION: ClinicalTrials.gov, ID: NCT02323412 . Registered on 21 November 2014.

Changes in gene expression of Zif, c-fos and cyclooxygenase-2 associated with spinal long-term potentiation.

Spinal cord long-term potentiation is often studied as a model for cellular memory of nociceptive information. In the present report, extracellular single-unit recordings and quantitative real-time reverse transcriptase polymerase chain reaction were used to examine whether the induction of spinal cord long-term potentiation involves changes in expression of Zif, c-fos and cyclooxygenase-2. The data demonstrated that induction of spinal cord long-term potentiation was associated with a transient increase in the expression of Zif at 120 min (p < 0.05, long-term potentiation group vs. control group). In contrast, a decrease or no changes were observed in the expression of c-fos and cyclooxygenase-2. The transient increase of the expression of Zif is consistent with an involvement in the transition from the early to the late-phase of spinal cord long-term potentiation.

Genetic analysis for a shared biological basis between migraine and coronary artery disease.

OBJECTIVE: To apply genetic analysis of genome-wide association data to study the extent and nature of a shared biological basis between migraine and coronary artery disease (CAD). METHODS: Four separate methods for cross-phenotype genetic analysis were applied on data from 2 large-scale genome-wide association studies of migraine (19,981 cases, 56,667 controls) and CAD (21,076 cases, 63,014 controls). The first 2 methods quantified the extent of overlapping risk variants and assessed the load of CAD risk loci in migraineurs. Genomic regions of shared risk were then identified by analysis of covariance patterns between the 2 phenotypes and by querying known genome-wide significant loci. RESULTS: We found a significant overlap of genetic risk loci for migraine and CAD. When stratified by migraine subtype, this was limited to migraine without aura, and the overlap was protective in that patients with migraine had a lower load of CAD risk alleles than controls. Genes indicated by 16 shared risk loci point to mechanisms with potential roles in migraine pathogenesis and CAD, including endothelial dysfunction (PHACTR1) and insulin homeostasis (GIP). CONCLUSIONS: The results suggest that shared biological processes contribute to risk of migraine and CAD, but surprisingly this commonality is restricted to migraine without aura and the impact is in opposite directions. Understanding the mechanisms underlying these processes and their opposite relationship to migraine and CAD may improve our understanding of both disorders.

The MMP1 rs1799750 2G allele is associated with increased low back pain, sciatica, and disability after lumbar disk herniation.

OBJECTIVES: Previous studies indicate that genetic variants in genes encoding proteins like matrix metalloproteinase (MMP) enzymes may affect degeneration of the intervertebral disk. One such genetic variant is a single nucleotide polymorphism insertion in the promoter region of the MMP1 gene, that is, the MMP1 rs1799750 2G allele, which increases the MMP1 expression in vitro. In this study, we examined whether the MMP1 rs1799750 2G allele might be associated with disk degeneration and clinical outcome after lumbar disk herniation. MATERIALS AND METHODS: A total of 260 patients with lumbar disk herniation and sciatic pain were included in this study and genotyped for the MMP1 rs1799750 2G allele. RESULTS: The present data showed no differences in the frequency of the MMP1 2G allele in patients recently diagnosed with disk herniation compared with pain-free controls. Moreover, in the patients, the MMP1 2G allele was not directly related to the disk degeneration. However, our data demonstrated that the MMP1 2G allele was associated with both pain and disability, that is, increased visual analog scale score, McGill Pain Questionnaire score, and Oswestry Disability Index score. Clearly, the patients homozygous for the 2G allele had more pain and reduced function compared with those carrying the 1G allele. DISCUSSIONS: Our findings suggest that the MMP1 rs1799750 2G/2G genotype may contribute to low back pain, sciatica, and disability after lumbar disk herniation.

Inhibition of fatty acid amide hydrolase (FAAH) reduces spinal nociceptive responses and expression of spinal long-term potentiation (LTP).

Fatty acid amide hydrolase (FAAH) is an enzyme that metabolizes endocannabinoids and fatty acid amides possibly linked to activation of the opioid system. To examine how this enzyme affects spinal signalling, electrophysiological recordings in the dorsal horn and qPCR on dorsal horn tissue following systemic administration of the FAAH inhibitor URB597 (0.3 and 1.0mg/kg i.v.) and spinal administration of the opioid receptor antagonist naloxone (0.1 µg/µl i.th.), were performed. The present data showed that the suppressive effect of the FAAH inhibitor URB597 (1.0mg/kg i.v.) on the spinal nociceptive responses was prevented by spinal administration of the opioid receptor antagonist naloxone (0.1 µg/µl i.th.). Moreover, the present findings demonstrated that the FAAH inhibitor URB597 (1.0mg/kg i.v.) partly reversed expression of spinal long-term potentiation (LTP) and also attenuated the LTP-associated increased Zif expression. We conclude that pharmacological inactivation of FAAH may be a promising strategy to inhibit the development of central hyperalgesia; thereby reinforcing the role of FAAH as a potential therapeutic target.

Spinal cord long-term potentiation (LTP) is associated with increased dorsal horn gene expression of IL-1beta, GDNF and iNOS.

Previous data show that spinal cord long-term potentiation (LTP) can be induced by electrical high-frequency stimulation (HFS) conditioning applied to the sciatic nerve. It has been suggested that the cellular events leading to this form of plasticity may contribute to central hyperalgesia. In the present study, extracellular recordings from single dorsal horn neurons and quantitative real-time reverse-transcriptase polymerase chain reaction (RT-PCR) on rat dorsal horn tissue were used to examine whether maintenance of spinal LTP is associated with changes in gene expression of the proinflammatory interleukin-1beta (IL-1beta), glial cell-line derived neurotrophic factor (GDNF), inducible nitric oxide synthase (iNOS), p38 mitogen-activated protein kinase (p38 MAPK), cyclooxygenase 2 (COX2) and tumor necrosis factor alpha (TNFalpha). The data demonstrated that the HFS conditioning induced a robust increase in the dorsal horn C-fibre responses, which outlasted the duration of the experiments of 6h (p<0.05, HFS vs. control). Moreover, a significant increase in the expression of mRNA for IL-1beta, GDNF and iNOS were observed 6h following the HFS conditioning (p<0.05, HFS vs. control). For the first time we show that spinal cord LTP is associated with an increased dorsal horn expression of the genes for IL-1beta, GDNF and iNOS.

Catechol-O-methyltransferase (COMT) inhibition reduces spinal nociceptive activity.

Several variants of the catechol-O-methyltransferase (COMT) gene have recently been linked to pain sensitivity. In the present study, electrophysiological field potential recordings from the dorsal horn in rats were used to examine the spinal effect of reduced COMT activity. The data demonstrated that 30 mg/kg of the COMT inhibitor OR 486 reduced spinal nociceptive responses to painful stimuli (p