Highly variable hearing loss due to POU4F3 (c.37del) is revealed by longitudinal, frequency specific analyses

Genotype-phenotype correlations add value to the management of families with hereditary hearing loss (HL), where age-related typical audiograms (ARTAs) are generated from cross-sectional regression equations and used to predict the audiogram phenotype across the lifespan. A seven-generation kindred with autosomal dominant sensorineural HL (ADSNHL) was recruited and a novel pathogenic variant in POU4F3 (c.37del) was identified by combining linkage analysis with whole exome sequencing (WES). POU4F3 is noted for large intrafamilial variation including the age of onset of HL, audiogram configuration and presence of vestibular impairment. Sequential audiograms and longitudinal analyses reveal highly variable audiogram features among POU4F3 (c.37del) carriers, limiting the utility of ARTAs for clinical prognosis and management of HL. Furthermore, a comparison of ARTAs against three previously published families (1 Israeli Jewish, 2 Dutch) reveals significant interfamilial differences, with earlier onset and slower deterioration. This is the first published report of a North American family with ADSNHL due to POU4F3, the first report of the pathogenic c.37del variant, and the first study to conduct longitudinal analysis, extending the phenotypic spectrum of DFNA15.

Practice guidelines for BRCA1/2 tumour testing in ovarian cancer

The purpose of this document is to provide pre-analytical, analytical and post-analytical considerations and recommendations to Canadian clinical laboratories developing, validating and offering next-generation sequencing (NGS)-based BRCA1 and BRCA2 (BRCA1/2) tumour testing in ovarian cancers. This document was drafted by the members of the Canadian College of Medical Geneticists (CCMG) somatic BRCA Ad Hoc Working Group, and representatives from the Canadian Association of Pathologists. The document was circulated to the CCMG members for comment. Following incorporation of feedback, this document has been approved by the CCMG board of directors. The CCMG is a Canadian organisation responsible for certifying medical geneticists and clinical laboratory geneticists, and for establishing professional and ethical standards for clinical genetics services in Canada. The current CCMG Practice Guidelines were developed as a resource for clinical laboratories in Canada; however, they are not inclusive of all information laboratories should consider in the validation and use of NGS for BRCA1/2 tumour testing in ovarian cancers.

Autosomal dominant non-syndromic hearing loss maps to DFNA33 (13q34) and co-segregates with splice and frameshift variants in ATP11A, a phospholipid flippase gene

Sequencing exomes/genomes have been successful for identifying recessive genes; however, discovery of dominant genes including deafness genes (DFNA) remains challenging. We report a new DFNA gene, ATP11A, in a Newfoundland family with a variable form of bilateral sensorineural hearing loss (SNHL). Genome-wide SNP genotyping linked SNHL to DFNA33 (LOD = 4.77), a locus on 13q34 previously mapped in a German family with variable SNHL. Whole-genome sequencing identified 51 unremarkable positional variants on 13q34. Continuous clinical ascertainment identified several key recombination events and reduced the disease interval to 769 kb, excluding all but one variant. ATP11A (NC_000013.11: chr13:113534963G>A) is a novel variant predicted to be a cryptic donor splice site. RNA studies verified in silico predictions, revealing the retention of 153 bp of intron in the 3' UTR of several ATP11A isoforms. Two unresolved families from Israel were subsequently identified with a similar, variable form of SNHL and a novel duplication (NM_032189.3:c.3322_3327+2dupGTCCAGGT) in exon 28 of ATP11A extended exon 28 by 8 bp, leading to a frameshift and premature stop codon (p.Asn1110Valfs43Ter). ATP11A is a type of P4-ATPase that transports (flip) phospholipids from the outer to inner leaflet of cell membranes to maintain asymmetry. Haploinsufficiency of ATP11A, the phospholipid flippase that specially transports phosphatidylserine (PS) and phosphatidylethanolamine (PE), could leave cells with PS/PE at the extracellular side vulnerable to phagocytic degradation. Given that surface PS can be pharmaceutically targeted, hearing loss due to ATP11A could potentially be treated. It is also likely that ATP11A is the gene underlying DFNA33.

Clinical and molecular significance of genetic loci associated with psoriatic arthritis

Psoriatic arthritis (PsA) is caused by a combination of environmental and multiple genetic factors, with clear evidence for a strong genetic basis. The remarkable accumulation of knowledge gained from genetic, pharmacogenetic, and therapeutic response of biologic agents in PsA has fundamentally changed and advanced our understanding of disease pathogenesis and has identified key signalling pathways. However, only one-quarter of the genetic contribution of PsA has been accounted for; and dissecting the genetic contributors of the cutaneous disease from those that would identify joint disease has been challenging. More importantly, the clinical utility of multiple proposed loci is unclear. In this review, we summarize the potential clinical relevance from established genetic associations and provide insight on the proposed molecular pathways that arise from these associations.

Rho-GTPase pathways may differentiate treatment response to TNF-alpha and IL-17A inhibitors in psoriatic arthritis

Biological therapies have dramatically improved the therapeutic landscape of psoriatic arthritis (PsA); however, 40–50% of patients are primary non-responders with response rates declining significantly with each successive biological therapy. Therefore, there is a pressing need to develop a coherent strategy for effective initial and subsequent selection of biologic agents. We interrogated 40 PsA patients initiating either tumour necrosis factor inhibitors (TNFi) or interleukin-17A inhibitors (17Ai) for active PsA. Patients achieving low disease activity according to the Disease Activity Index for PsA (DAPSA) at 3 months were classified as responders. Baseline and 3-month CD4⁺ transcript profiling were performed, and novel signaling pathways were identified using a multi-omics profiling and integrative computational analysis approach. Using transcriptomic data at initiation of therapy, we identified over 100 differentially expressed genes (DEGs) that differentiated IL-17Ai response from non-response and TNFi response from non-response. Integration of cell-type-specific DEGs with protein–protein interactions and further comprehensive pathway enrichment analysis revealed several pathways. Rho GTPase signaling pathway exhibited a strong signal specific to IL-17Ai response and the genes, RAC1 and ROCKs, are supported by results from prior research. Our detailed network and pathway analyses have identified the rewiring of Rho GTPase pathways as potential markers of response to IL17Ai but not TNFi. These results need further verification.

The Genetics of Psoriasis and Psoriatic Arthritis

Psoriatic arthritis (PsA) is an inflammatory arthritis that manifests in 20-30% of patients diagnosed with psoriasis. Epidemiologic studies suggest a substantial genetic contribution to PsA. There is a strong need for genome-wide association studies on patients with PsA, including PsA-weighted or specific variants, and a need for a better understanding of the relevance of HLA alleles in disease expression. Interferon signaling and the nuclear factor-κB cascade are involved in PsA, and there are genetic differences between purely cutaneous psoriasis (PsC) and PsA. Psoriasis susceptibility genes for which putative functional coding variants in TYK2 and TRAF3IP2 are strongly associated with PsC and PsA, and neutrophil extracellular traps promote Th17 induction in an Act1 D10N-dependent fashion. Genomics and serological factors may also predict treatment response in tumor necrosis factor inhibitors (TNFi) in PsA, and genetics may play a role in treatment response to TNFi. Collaborations through the Group for Research and Assessment of Psoriasis and Psoriatic Arthritis (GRAPPA) are essential to increase study population size, which will enhance the ability to detect the genetic variants that create a predisposition to psoriatic disease and to predict response to biological therapy.

A dominant RAD51C pathogenic splicing variant predisposes to breast and ovarian cancer in the Newfoundland population due to founder effect

Background

RAD51C is important in DNA repair and individuals with pathogenic RAD51C variants have increased risk of hereditary breast and ovarian cancer syndrome (HBOC), an autosomal dominant genetic predisposition to early onset breast and/or ovarian cancer.

Methods

Five female HBOC probands sequenced negative for moderate‐ and high‐risk genes but shared a recurrent variant of uncertain significance in RAD51C (NM_058216.3: c.571 + 4A > G). Participant recruitment was followed by haplotype and case/control analyses, RNA splicing analysis, gene and protein expression assays, and Sanger sequencing of tumors.

Results

The RAD51C c.571 + 4A > G variant segregates with HBOC, with heterozygotes sharing a 5.07 Mbp haplotype. RAD51C c.571 + 4A > G is increased ~52‐fold in the Newfoundland population compared with the general Caucasian population and positive population controls share disease‐associated alleles, providing evidence of a founder effect. Splicing analysis confirmed in silico predictions that RAD51C c.571 + 4A > G causes exon 3 skipping, creating an immediate premature termination codon. Gene and protein expression were significantly reduced in a RAD51C c.571 + 4G > A heterozygote compared with a wild‐type relative. Sanger sequencing of tumors from two probands indicates loss‐of‐heterozygosity, suggesting loss of function.

Conclusion

The RAD51C c.571 + 4A > G variant affects mRNA splicing and should be re‐classified as pathogenic according to American College of Medical Genetics and Genomics guidelines.

Novel Usher syndrome pathogenic variants identified in cases with hearing and vision loss

Background

Usher syndrome, the most common form of inherited deaf-blindness, is unlike many other forms of syndromic hereditary hearing loss in that the extra aural clinical manifestations are also detrimental to communication. Usher syndrome patients with early onset deafness also experience vision loss due to progressive retinitis pigmentosa that can lead to legal blindness in their third or fourth decade.

Methods

Using a multi-omic approach, we identified three novel pathogenic variants in two Usher syndrome genes (USH2A and ADGRV1) in cases initially referred for isolated vision or hearing loss.

Results

In a multiplex hearing loss family, two affected sisters, the product of a second cousin union, are homozygous for a novel nonsense pathogenic variant in ADGRV1 (c.17062C > T, p.Arg5688*), predicted to create a premature stop codon near the N-terminus of ADGRV1. Ophthalmological examination of the sisters confirmed typical retinitis pigmentosa and prompted a corrected Usher syndrome diagnosis. In an unrelated clinical case, a child with hearing loss tested positive for two novel USH2A splicing variants (c.5777-1G > A, p. Glu1926_Ala1952del and c.10388-2A > G, p.Asp3463Alafs*6) and RNA studies confirmed that both pathogenic variants cause splicing errors. Interestingly, these same USH2A variants are also identified in another family with vision loss where subsequent clinical follow-up confirmed pre-existing hearing loss since early childhood, eventually resulting in a reassigned diagnosis of Usher syndrome.

Conclusion

These findings provide empirical evidence to increase Usher syndrome surveillance of at-risk children. Given that novel antisense oligonucleotide therapies have been shown to rescue retinal degeneration caused by USH2A splicing pathogenic variants, these solved USH2A patients may now be eligible to be enrolled in therapeutic trials.

A review of ixekizumab in the treatment of psoriatic arthritis

INTRODUCTION

Psoriatic arthritis (PsA) is a heterogeneous inflammatory disorder with articular, peri-articular, and extra-articular features along with selected co-morbidities as a sequela to chronic inflammation. There is accumulating evidence that the Th-17 signaling pathway is of critical importance in PsA pathogenesis. Areas covered: Ixekizumab (IXE) is a humanized immunoglobulin G subclass 4 (IgG4) monoclonal antibody directed against IL-17A. Two phase III randomized clinical trials, SPIRIT-P1 and SPIRIT-P2, unequivocally demonstrated superiority of IXE (80 mg every two or 4 weeks) dosing over placebo in moderate-to-severe PsA patients that failed either NSAIDs, conventional disease-modifying anti-rheumatic drugs (csDMARDs), or tumor necrosis factor-α inhibitors (TNFi) for numerous articular and cutaneous parameters. IXE also delayed structural progression of PsA. No new safety signals were identified as compared with chronic plaque psoriasis studies which included many more patients. Expert opinion: IXE is a highly effective treatment for moderate to severe PsA patients, including those that have been previously exposed to csDMARD and TNFi. Most domains of PsA significantly improved with IXE treatment and disease modification was achieved.

Ustekinumab in psoriatic arthritis and related phenotypes

Psoriatic arthritis (PsA) is an inflammatory arthritis that commonly occurs with psoriasis and is attributed to genetic, immunologic and environmental factors. The T-helper (Th)-17 pathway and the interleukin (IL)-23/IL-17 axis have become prominent players in PsA and considerably increased our understanding of disease pathogenesis. In this review article, we will focus on the emerging role of IL-12/23 and its blockade, in the pathogenesis and management of PsA as well as of psoriasis and inflammatory bowel disease. Ustekinumab, is a fully human monoclonal immunoglobulin (Ig)G1 antibody that binds specifically to the p40 subunit of IL-12 and IL-23, primarily inhibiting downstream Th-17 signalling pathways. Ustekinumab produced consistent and sustained clinical efficacy in two phase III clinical trials in PsA, PSUMMIT-1 and PSUMMIT-2, with data out to 52 weeks, and no new safety signals. PSUMMIT-1 included patients with active PsA despite conventional therapy who were all naïve to anti-tumour necrosis factor (TNF) agents, whereas PSUMMIT-2 also included anti-TNF experienced patients. Similarly, ustekinumab produced consistent clinical efficacy in two phase III clinical trials in psoriasis, PHOENIX-1 and PHOENIX-2, and in both induction and maintenance of moderate-to-severe Crohn's disease, UNITI-1, UNITI-2 and IM-UNITI, without an increased safety signal. Currently, ustekinumab is used in the treatment of PsA following the failure of nonsteroidal anti-inflammatory drugs (NSAIDs) and conventional disease-modifying antirheumatic drugs (DMARDs), and as an alternative to, or after failure of an anti-TNF agent.

A review of ustekinumab in the treatment of psoriatic arthritis

Psoriatic arthritis is an inflammatory arthritis associated with psoriasis. The IL-23/IL-17 axis is an important pathway in the development of psoriatic disease. Ustekinumab is a fully human monoclonal IgG1 antibody that binds to the p40 subunit of IL-12 and IL-23, which, in turn, inhibits downstream signaling pathways. PSUMMIT-1 and PSUMMIT-2 are two pivotal Phase III trials demonstrating global improvement in primary and secondary outcomes including inhibition of radiographic progression. Therapeutic benefit of ustekinumab for synovitis appears independent of previous disease modifying antirheumatic disease or anti-TNF exposure. At present, the data support the use of ustekinumab in the treatment of psoriatic arthritis after the failure of NSAIDs and conventional disease modifying antirheumatic diseases as an alternative to, or after failure of an anti-TNF agent.

A common variant in CLDN14 causes precipitous, prelingual sensorineural hearing loss in multiple families due to founder effect

Genetic isolates provide unprecedented opportunities to identify pathogenic mutations and explore the full natural history of clinically heterogeneous phenotypes such as hearing loss. We noticed a unique audioprofile, characterized by prelingual and rapid deterioration of hearing thresholds at frequencies >0.5 kHz in several adults from unrelated families from the island population of Newfoundland. Targeted serial Sanger sequencing of probands for deafness alleles (n = 23) that we previously identified in this founder population was negative. Whole exome sequencing in four members of the largest family (R2010) identified a CLDN14 (DFNB29) variant [c.488C>T; p. (Ala163Val)], likely pathogenic, sensorineural hearing loss, autosomal recessive. Although not associated with deafness or disease, CLDN14 p.(Ala163Val) has been previously reported as a variant of uncertain significance (VUS). Targeted sequencing of 169 deafness probands identified one homozygote and one heterozygous carrier. Genealogical studies, cascade sequencing and haplotype analysis across four unrelated families showed all subjects with the unique audioprofile (n = 12) were also homozygous for p.(Ala163Val) and shared a 1.4 Mb DFNB29-associated haplotype on chromosome 21. Most significantly, sequencing 175 population controls revealed 1% of the population are heterozygous for CLDN14 p.(Ala163Val), consistent with a major founder effect in Newfoundland. The youngest CLDN14 [c.488C>T; p.(Ala163Val)] homozygote passed newborn screening and had normal hearing thresholds up to 3 years of age, which then deteriorated to a precipitous loss >1 kHz during the first decade. Our study suggests that genetic testing may be necessary to identify at-risk children in time to prevent speech, language and developmental delay.

Pharmacogenetics and pharmacogenomics in psoriasis treatment: current challenges and future prospects

INTRODUCTION

Topical, systemic, oral disease modifying, and biologic agents are part of the armamentarium to manage psoriatic disease. The choice of therapy depends upon disease severity, relevant co-morbidities and patient preference. There is great variability in patient response with these agents, and there is still no clear method of selecting the preferred therapeutic agent for efficacy or lack of adverse events.

AREAS COVERED

This article will review the pharmacogenetic and pharmacogenomic targets that are currently known with respect to psoriasis vulgaris, and the most frequent co-morbidity of psoriasis, psoriatic arthritis.

EXPERT OPINION

Presently, no clinically actionable biomarker exists for any therapeutic agent used to treat psoriasis or psoriatic arthritis. The lack of validated outcome measures and conflicting results of open-label studies conducted may be attributed to a multitude of issues that confound discovery. Consequently, studies have been underpowered to identify genes or genetic variants worth translating to clinical practice. In order to achieve a pharmacogenetic/pharmacogenomic signature, improvements in study design of future investigations are required, including carefully designed prospective studies. It is imperative to combine known clinical, serological, and molecular markers with consistent outcomes and an adequate health economic evaluation before they can be adopted widely in clinical practice.

Genetic, Epigenetic and Pharmacogenetic Aspects of Psoriasis and Psoriatic Arthritis

There is a strong familial component to psoriatic disease as well as a complex array of genetic, immunologic, and environmental factors. The dominant genetic effect is located on chromosome 6p21.3 within the major histocompatibility complex region, accounting for one-third of genetic contribution. Genome-wide association studies (GWAS) identified additional genes, including skin barrier function, innate immune response, and adaptive immune response genes. To better understand disease susceptibility and progression requires replication in larger cohorts, fine-mapping efforts, new technologies, and functional studies of genetic variants, gene-gene interactions and gene-environmental interactions. New technologies available include next-generation sequencing, copy number variation analysis, and epigenetics.

Private rare deletions in SEC16A and MAMDC4 may represent novel pathogenic variants in familial axial spondyloarthritis

Objective

Axial spondyloarthritis (AxSpA) represents a group of inflammatory axial diseases that share common clinical and histopathological manifestations. Ankylosing spondylitis (AS) is the best characterised subset of AxSpA, and its genetic basis has been extensively investigated. Given that genome-wide association studies account for only 25% of AS heritability, the objective of this study was to discover rare, highly penetrant genetic variants in AxSpA pathogenesis using a well-characterised, multigenerational family.

Methods

HLA-B*27 genotyping and exome sequencing was performed on DNA collected from available family members. Variant frequency was assessed by mining publically available datasets and using fragment analysis of unrelated AxSpA cases and unaffected controls. Gene expression was performed by qPCR, and protein expression was assessed by western blot analysis and immunofluorescence microscopy using patient-derived B-cell lines. Circular dichroism spectroscopy was performed to assess the impact of discovered variants on secondary structure.

Results

This is the first report identifying two rare private familial variants in a multigenerational AxSpA family, an in-frame SEC16A deletion and an out-of-frame MAMDC4 deletion. Evidence suggests the causative mechanism for SEC16A appears to be a conformational change induced by deletion of three highly conserved amino acids from the intrinsically disordered Sec16A N-terminus and RNA-mediated decay for MAMDC4.

Conclusions

The results suggest that it is the presence of rare syntenic SEC16A and MAMDC4 deletions that increases susceptibility to AxSpA in family members who carry the HLA-B*27 allele.

Clinical genetic research 2: Genetic epidemiology of complex phenotypes

Genetic factors play a substantive role in the susceptibility to common diseases. Due to recent and rapid advancements in characterization of genetic variants and large-scale genotyping platforms, multiple genes and genetic variants have now been identified for common, complex diseases. The most efficient method for gene identification at present appears to be large-scale association-based studies, which integrate genetic and epidemiological principles. As the strategy for gene identification studies has shifted towards genetic association-based methods rather than traditional linkage analysis, epidemiological methods are increasingly being integrated into genetic investigations. Consequently, the disciplines of genetics and epidemiology, which historically have functioned separately, have been integrated into a discipline referred to as genetic epidemiology. In this chapter, we review methods for establishing the genetic burden of complex genetic disease, followed by methods for gene and/or genetic variant identification and when appropriate we highlight the epidemiological issues that guide these methods.

Genome-wide signatures of 'rearrangement hotspots' within segmental duplications in humans

The primary objective of this study was to create a genome-wide high resolution map (i.e., >100 bp) of ‘rearrangement hotspots’ which can facilitate the identification of regions capable of mediating de novo deletions or duplications in humans. A hierarchical method was employed to fragment segmental duplications (SDs) into multiple smaller SD units. Combining an end space free pairwise alignment algorithm with a ‘seed and extend’ approach, we have exhaustively searched 409 million alignments to detect complex structural rearrangements within the reference-guided assembly of the NA18507 human genome (18× coverage), including the previously identified novel 4.8 Mb sequence from de novo assembly within this genome. We have identified 1,963 rearrangement hotspots within SDs which encompass 166 genes and display an enrichment of duplicated gene nucleotide variants (DNVs). These regions are correlated with increased non-allelic homologous recombination (NAHR) event frequency which presumably represents the origin of copy number variations (CNVs) and pathogenic duplications/deletions. Analysis revealed that 20% of the detected hotspots are clustered within the proximal and distal SD breakpoints flanked by the pathogenic deletions/duplications that have been mapped for 24 NAHR-mediated genomic disorders. FISH Validation of selected complex regions revealed 94% concordance with in silico localization of the highly homologous derivatives. Other results from this study indicate that intra-chromosomal recombination is enhanced in genic compared with agenic duplicated regions, and that gene desert regions comprising SDs may represent reservoirs for creation of novel genes. The generation of genome-wide signatures of ‘rearrangement hotspots’, which likely serve as templates for NAHR, may provide a powerful approach towards understanding the underlying mutational mechanism(s) for development of constitutional and acquired diseases.

Pharmacogenetics of rheumatoid arthritis: Potential targets from susceptibility genes and present therapies

Rheumatoid arthritis (RA) is a chronic heterogeneous autoimmune disorder of unknown etiology resulting in inflammation in the synovium, cartilage, and bone. Genetic factors play an important role in susceptibility to RA as the heritability of RA is between 50% and 60%, with the human leukocyte antigen (HLA) locus accounting for at least 30% of overall genetic risk. Outside the major histocompatibility complex (MHC) region, six additional risk loci have been identified and validated including PTPN22, STAT4, PADI4, CTLA4, TNFAIP3-OLIG3, and TRAF1/C5. Genetic factors are also important in RA pharmacotherapy due to the gene-dependent activity of enzymes involved in the pharmacokinetics and/or pharmacodynamics of RA medications. Indeed, there is great variability in drug efficacy as well as adverse events associated with any anti-rheumatic therapy and genetics is thought to contribute significantly to this inter-individual variability in response. This review will summarize the genetic factors that have been implicated in the pathogenesis of RA, and how these determinants may factor into the potential pharmacogenetics of this disease. We will also review the therapeutic agents that are currently being utilized or presently being evaluated in the treatment of RA, along with potential pharmacogenetic markers that have been proposed for such medications.

Spinal nerve ligation-induced activation of nuclear factor kappaB is facilitated by prostaglandins in the affected spinal cord and is a critical step in the development of mechanical allodynia

This study investigated the effect of 5th and 6th lumbar nerve (L5/L6) spinal nerve ligation (SNL) on activated nuclear factor kappaB (NFkBa) in nuclear extracts from the lumbar dorsal horn of the rat, and its relationship to prostaglandin (PG)-dependent spinal hyperexcitability and allodynia 3 days later. Male Sprague-Dawley rats, fitted with intrathecal (i.t.) catheters, underwent SNL- or sham-surgery. Paw withdrawal threshold (PWT), electromyographic analysis of the biceps femoris flexor reflex, and immunoblotting of the spinal cord were used. Both allodynia (PWT <or=4 g) and exaggerated A- and C-fiber-mediated reflex responses (AFRR and CFRR), featuring decreased activation thresholds and evoked hyperexcitability, were evident only in nerve-ligated animals. This was preceded by an increase in NFkBa in the ipsilateral lumbar dorsal horn at 12 h which was still present 3 days after SNL. The amount of NFkBa in the ventral horns was unchanged compared with sham-controls. Blocking the activation of spinal NFkappaB, either directly with ammonium pyrrolidedithiocarbamate (PDTC; 100 microg i.t.) or indirectly with S(+)-ibuprofen (100 microg i.t.) administered immediately after SNL, prevented the SNL-induced expression of spinal cyclooxygenase-2 and the development of spinal hyperexcitability and allodynia 3 days later. R(-)-Ibuprofen and vehicle had no effect. These results demonstrate that NFkappaB is not only activated by SNL, but that spinal PG generated in the affected spinal cord from the onset of nerve injury facilitates this process. NFkappaB is a critical antecedent in the development of spinal PG-dependent hyperexcitability and allodynia in the SNL model.

Spinal Prostaglandins Facilitate Exaggerated A- and C-fiber-mediated Reflex Responses and Are Critical to the Development of Allodynia Early after L5-L6 Spinal Nerve Ligation

Background

Spinal prostaglandins are important in the early pathogenesis of spinal nerve ligation (SNL)-induced allodynia. This study examined the effect of SNL on the expression of cyclooxygenase (COX)-1, COX-2, and prostaglandin E2 receptors in the rat lumbar spinal cord, and the temporal and pharmacologic relation of these changes to the exaggerated A- and C-fiber-mediated reflex responses and allodynia, 24 h after injury.

Methods

Male Sprague-Dawley rats, fitted with intrathecal catheters, underwent SNL or sham surgery. Paw withdrawal threshold, electromyographic analysis of the biceps femoris flexor reflex, and immunoblotting of the spinal cord were used.

Results

Both allodynia (paw withdrawal threshold of &lt; or = 4 g) and exaggerated A- and C-fiber-mediated reflex responses (i.e., decrease in activation threshold, increase in evoked activity, including windup; P &lt; 0.05) were evident 24 h after SNL but not sham surgery. Allodynic animals exhibited significant increases in prostaglandin E2 receptor (subtypes 1-3) and COX-1 (but not COX-2) expression in the ipsilateral lumbar dorsal horn. The corresponding ventral horns and contralateral dorsal horn were unchanged from sham controls. Exaggerated A- and C-fiber-mediated reflex responses were significantly attenuated by intrathecal SC-560 or SC-51322, but not SC-236, given 24 h after SNL.

Conclusion

These results provide further evidence that spinal prostaglandins, derived primarily from COX-1, are critical in the exaggeration of A- and C-fiber input and allodynia, 24 h after SNL.

Increased Expression of Cyclooxygenase and Nitric Oxide Isoforms, and Exaggerated Sensitivity to Prostaglandin E2, in the Rat Lumbar Spinal Cord 3 Days after L5–L6 Spinal Nerve Ligation

Background

Spinal prostaglandins seem to be important in the early pathogenesis of experimental neuropathic pain. Here, the authors investigated changes in the expression of cyclooxygenase and nitric oxide synthase (NOS) isoforms in the lumbar, thoracic, and cervical spinal cord and the pharmacologic sensitivity to spinal prostaglandin E2 (PGE2) after L5-L6 spinal nerve ligation (SNL).

Methods

Male Sprague-Dawley rats, fitted with intrathecal catheters, underwent SNL or sham surgery 3 days before experimentation. Paw withdrawal threshold was monitored for up to 20 days. Immunoblotting, spinal glutamate release, and behavioral testing were examined 3 days after SNL.

Results

Allodynia (paw withdrawal threshold &lt; or = 4 g) was evident 1 day after SNL and remained stable for 20 days. Paw withdrawal threshold was unchanged (P &gt; 0.05) from baseline (&gt; 15 g) after sham surgery except for a small but significant decrease on day 20. Cyclooxygenase 2, neuronal NOS, and inducible NOS were significantly increased in the ipsilateral lumbar dorsal horn after SNL. Expression in the contralateral dorsal horn and ventral horns (lumbar segments) or bilaterally (thoracic and cervical segments) was unchanged from sham controls. This was accompanied by a significant decrease in both the EC50 of PGE2-evoked glutamate release and the ED50 of PGE2 on brush-evoked allodynia. Enhanced sensitivity to PGE2 was localized to lumbar segments of SNL animals and attenuated by SC-51322 or S(+)-ibuprofen, but not R(-)-ibuprofen (100 mum).

Conclusion

The increased expression of cyclooxygense-2, neuronal NOS, and inducible NOS and the enhanced sensitivity to PGE2 in spinal segments affected by SNL support the hypothesis that spinal prostanoids play an early pathogenic role in experimental neuropathic pain.

Inhibition of Spinal Prostaglandin Synthesis Early after L5/L6 Nerve Ligation Prevents the Development of Prostaglandin-dependent and Prostaglandin-independent Allodynia in the Rat

Background

Prostaglandins, synthesized in the spinal cord in response to noxious stimuli, are known to facilitate nociceptive transmission, raising questions about their role in neuropathic pain. The current study tested the hypothesis that spinal nerve ligation-induced allodynia is composed of an early prostaglandin-dependent phase, the disruption of which prevents allodynia.

Methods

Male Sprague-Dawley rats, fitted with intrathecal drug delivery or microdialysis catheters, underwent left L5-L6 spinal nerve ligation or sham surgery. Paw withdrawal threshold, brush-evoked behavior, and the concentration of prostaglandin E2 (PGE2) in spinal cerebrospinal fluid ([PGE2]dialysate) were determined for up to 24 days. PGE2-evoked glutamate release from spinal slices was also determined.

Results

Paw withdrawal threshold decreased from at least 15 g (control) to less than 4 g, beginning 1 day after ligation. Brushing the affected hind paw evoked nociceptive-like behavior and increased [PGE2]dialysate (up to 257 +/- 62% of baseline). There was no detectable change in basal [PGE2]dialysate from preligation values. The EC50 of PGE2-evoked glutamate release (2.4 x 10-11 M, control) was significantly decreased in affected spinal segments of allodynic rats (8.9 x 10-15 M). Treatment with intrathecal S(+)-ibuprofen or SC-560, beginning 2 h after ligation, prevented the decrease in paw withdrawal threshold, the brush-evoked increase in [PGE2]dialysate, and the change in EC50 of PGE2-evoked glutamate release. R(-)-ibuprofen or SC-236 had no effect.

Conclusions

The results of this study provide solid evidence that spinal prostaglandins, synthesized by cyclooxygenase-1 in the first 4-8 h after ligation, are critical in the pathogenesis of prostaglandin-dependent and prostaglandin-independent allodynia and that their early pharmacologic disruption affords protection against this neuropathic state in the rat.