Pain perception is altered by a nucleotide polymorphism in SCN9A.

The gene SCN9A is responsible for three human pain disorders. Nonsense mutations cause a complete absence of pain, whereas activating mutations cause severe episodic pain in paroxysmal extreme pain disorder and primary erythermalgia. This led us to investigate whether single nucleotide polymorphisms (SNPs) in SCN9A were associated with differing pain perception in the general population. We first genotyped 27 SCN9A SNPs in 578 individuals with a radiographic diagnosis of osteoarthritis and a pain score assessment. A significant association was found between pain score and SNP rs6746030; the rarer A allele was associated with increased pain scores compared to the commoner G allele (P = 0.016). This SNP was then further genotyped in 195 pain-assessed people with sciatica, 100 amputees with phantom pain, 179 individuals after lumbar discectomy, and 205 individuals with pancreatitis. The combined P value for increased A allele pain was 0.0001 in the five cohorts tested (1277 people in total). The two alleles of the SNP rs6746030 alter the coding sequence of the sodium channel Nav1.7. Each was separately transfected into HEK293 cells and electrophysiologically assessed by patch-clamping. The two alleles showed a difference in the voltage-dependent slow inactivation (P = 0.042) where the A allele would be predicted to increase Nav1.7 activity. Finally, we genotyped 186 healthy females characterized by their responses to a diverse set of noxious stimuli. The A allele of rs6746030 was associated with an altered pain threshold and the effect mediated through C-fiber activation. We conclude that individuals experience differing amounts of pain, per nociceptive stimulus, on the basis of their SCN9A rs6746030 genotype.

Rofecoxib regulates the expression of genes related to the matrix metalloproteinase pathway in humans: implication for the adverse effects of cyclooxygenase-2 inhibitors.

BACKGROUND: Cyclooxygenase-2 (COX-2) and COX-2-derived prostaglandins contribute to acute inflammation and pain, as well as resolution of inflammation; inhibition of COX-2 results in persistence of inflammation. Because matrix metalloproteinases (MMPs) play an essential role in inflammatory tissue injury and their activity is regulated by COX-2-derived prostaglandin E2, we evaluated whether COX-2 inhibition is associated with MMP overexpression during acute inflammation. METHODS: A total of 102 oral mucosal biopsy specimens were taken from 51 healthy volunteers who required extraction of impacted third molars. Subjects randomly received either rofecoxib (50 mg daily), ibuprofen (400 mg 4 times per day), or placebo 90 minutes before surgery and up to 48 hours after surgery. Total ribonucleic acid extracted from each biopsy specimen was used to analyze changes in gene expression related to the MMP pathway after tissue injury and drug treatments by use of microarray and quantitative real-time polymerase chain reaction in this clinical model of acute inflammation. RESULTS: Following tissue injury, rofecoxib increased the expression of genes associated with degradation of the extracellular matrix, including MMP-1 (64.7 +/- 6.5, P = .010), MMP-3 (41.7 +/- 4.8, P = .007), PLAT (encoding tissue plasminogen activator) (10.9 +/- 4.6, P = .032), and IL8 (encoding interleukin 8) (8.3 +/- 6.7, P = .020), and decreased the expression of TIMP3 (encoding tissue inhibitor of metalloproteinase 3) (6.2 +/- 2.8, P = .027). Ibuprofen produced similar effects on the expression of MMP-1 (23.4 +/- 5.0, P = .016) and MMP-3 (26.3 +/- 4.2, P = .003). In contrast, the expression of these genes was not statistically changed after tissue injury in the placebo group. The microarray data were in concordance with the changes in gene expression confirmed by quantitative real-time polymerase chain reaction. CONCLUSION: These findings provide evidence at the transcriptional level that inhibition of COX-2, in the presence of acute inflammation, induces changes in gene expression related to the MMP pathway. These changes may contribute to the adverse effects attributed to COX-2 inhibition by interfering with resolution of inflammation.

Genetically mediated interindividual variation in analgesic responses to cyclooxygenase inhibitory drugs.

BACKGROUND: Wide interindividual variation in responses to cyclooxygenase (COX) inhibitory drugs limits their clinical utility and safety. METHODS: To better understand the molecular responses to COX inhibition, we analyzed the gene expression level of the genes encoding enzymes related to prostaglandin production including the COX-1 gene (PTGS1) and the COX-2 gene (PTGS2), as well as their genetic polymorphisms, and the analgesic response to COX inhibitory drugs such as ibuprofen or rofecoxib or to placebo after minor surgery. RESULTS: Notable heterogeneity in global gene expression was evident between subjects. At 2 to 4 hours after surgery, PTGS1 expression was slightly decreased (36%, P < .001) and PTGS2 expression was markedly increased (300%, P < .001) with wide interindividual variation; at 48 hours after surgery, little detectable change in PTGS1 and PTGS2 expression was found in the control group. However, ibuprofen and rofecoxib treatment significantly increased PTGS2 expression at 48 hours (P = .001 and P = .049, respectively). At 2 to 4 hours after surgery, patients with the G/G allele at the nucleotide position of -765G>C in PTGS2 showed a significantly higher increase in PTGS2 expression (P = .012) compared with G/C and C/C patients, although all of them showed an increase in PTGS2 expression (P < .001 and P = .043, respectively). Among G/G patients, rofecoxib administration resulted in significantly lower pain intensity on a visual analog scale (7.2 +/- 2.5 mm) (P = .008) at 48 hours after surgery, as compared with ibuprofen administration (31.3 +/- 6.7 mm). The finding regarding pain intensity at 48 hours in G/C and C/C patients was opposite (P = .002), being greater in the rofecoxib group (37 +/- 6.8 mm) compared with the ibuprofen group (7 +/- 1.9 mm). CONCLUSIONS: These results suggest that wide variability in gene expression and functional polymorphisms in PTGS2 may explain part of the interindividual variations in acute pain and the analgesic efficacy of nonsteroidal anti-inflammatory drugs and selective COX-2 inhibitors; this may be useful to define individual responders on the basis of genetic variations to predict patient risk and benefit to drugs.

Upregulation of IL-6, IL-8 and CCL2 gene expression after acute inflammation: Correlation to clinical pain.

Tissue injury initiates a cascade of inflammatory mediators and hyperalgesic substances including prostaglandins, cytokines and chemokines. Using microarray and qRT-PCR gene expression analyses, the present study evaluated changes in gene expression of a cascade of cytokines following acute inflammation and the correlation between the changes in the gene expression level and pain intensity in the oral surgery model of tissue injury and acute pain. Tissue injury resulted in a significant upregulation in the gene expression of interleukin-6 (IL-6; 63.3-fold), IL-8 (8.1-fold), chemokine (C-C motif) ligand 2 (CCL2; 8.9-fold), chemokine (C-X-C motif) ligand 1 (CXCL1; 30.5-fold), chemokine (C-X-C motif) ligand 2 (CXCL2; 26-fold) and annexin A1 (ANXA1; 12-fold). The upregulation of IL-6 gene expression was significantly correlated to the upregulation of IL-8, CCL2, CXCL1 and CXCL2 gene expression. Interestingly, the tissue injury-induced upregulation of IL-6, IL-8 and CCL2 gene expression, was positively correlated to pain intensity at 3h post-surgery, the onset of acute inflammatory pain. However, ketorolac treatment did not have a significant effect on the gene expression of IL-6, IL-8, CCL2, CXCL2 and ANXA1 at the same time point of acute inflammation. These results demonstrate that the upregulation of IL-6, IL-8 and CCL2 gene expression contributes to the development of acute inflammation and inflammatory pain. The lack of effect of ketorolac on the expression of these gene products may be related to the ceiling analgesic effects of non-steroidal anti-inflammatory drugs.

Rofecoxib modulates multiple gene expression pathways in a clinical model of acute inflammatory pain.

New insights into the biological properties of cyclooxygenase-2 (COX-2) and its response pathway challenge the hypothesis that COX-2 is simply pro-inflammatory and inhibition of COX-2 solely prevents the development of inflammation and ameliorates inflammatory pain. The present study performed a comprehensive analysis of gene/protein expression induced by a selective inhibitor of COX-2, rofecoxib, compared with a non-selective COX inhibitor, ibuprofen, and placebo in a clinical model of acute inflammatory pain (the surgical extraction of impacted third molars) using microarray analysis followed by quantitative RT-PCR verification and Western blotting. Inhibition of COX-2 modulated gene expression related to inflammation and pain, the arachidonic acid pathway, apoptosis/angiogenesis, cell adhesion and signal transduction. Compared to placebo, rofecoxib treatment increased the gene expression of ANXA3 (annexin 3), SOD2 (superoxide dismutase 2), SOCS3 (suppressor of cytokine signaling 3) and IL1RN (IL1 receptor antagonist) which are associated with inhibition of phospholipase A(2) and suppression of cytokine signaling cascades, respectively. Both rofecoxib and ibuprofen treatment increased the gene expression of the pro-inflammatory mediators, IL6 and CCL2 (chemokine C-C motif ligand 2), following tissue injury compared to the placebo treatment. These results indicate a complex role for COX-2 in the inflammatory cascade in addition to the well-characterized COX-dependent pathway, as multiple pathways are also involved in rofecoxib-induced anti-inflammatory and analgesic effects at the gene expression level. These findings may also suggest an alternative hypothesis for the adverse effects attributed to selective inhibition of COX-2.