Up-regulation of δ-opioid receptors and κ-opioid receptors in the skin of fibromyalgia patients

Fibromyalgia and Skin Disorders: A Systematic Review

Background: Fibromyalgia is a complex multifaceted syndrome primarily characterised by chronic musculoskeletal pain, fatigue, and functional symptoms. Although FM is known to be associated with several comorbidities, the aim of this systematic review was to comprehensively examine the available evidence regarding the relationship between FM and dermatological manifestations. Methods: We followed the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines, and MedLine and Web of Science (WOS) databases were searched up to June 2023. After removing duplicate records, 21 articles were deemed eligible for inclusion in the qualitative synthesis. Results: Overall, the included studies revealed an increased frequency of FM among patients with cutaneous diseases, including psoriasis, chronic urticaria, contact allergy, acneiform disorders, hidradenitis suppurativa, and vitiligo. Additionally, the presence of comorbid FM may intensify skin conditions, which has a negative impact on quality of life and vice versa. Conclusions: Although the causal mechanisms of FM are still far from being understood, this systematic review suggests a relationship between FM and skin disorders. However, further research is encouraged in this area.

A Comprehensive Review of the Genetic and Epigenetic Contributions to the Development of Fibromyalgia

This narrative review summarizes the current knowledge of the genetic and epigenetic contributions to the development of fibromyalgia (FM). Although there is no single gene that results in the development of FM, this study reveals that certain polymorphisms in genes involved in the catecholaminergic pathway, the serotonergic pathway, pain processing, oxidative stress, and inflammation may influence susceptibility to FM and the severity of its symptoms. Furthermore, epigenetic changes at the DNA level may lead to the development of FM. Likewise, microRNAs may impact the expression of certain proteins that lead to the worsening of FM-associated symptoms.

Dual-Acting Peripherally Restricted Delta/Kappa Opioid (CAV1001) Produces Antinociception in Animal Models of Sub-Acute and Chronic Pain

Background

The development of highly efficacious alternatives to mu-opioid analgesics represents an urgent unmet medical and public health need. In the presence of inflammation both delta- and kappa-opioid agonists, acting on peripheral sensory neurons, mediate analgesia. The dual-acting, peripherally restricted kappa/delta-opioid agonist, CAV1001, was tested in four rodent pain models.

Methods

Experiment 1 – Formalin testing in mice. Three doses (1–10 mg/kg) of CAV1001 or ICI204448 at 30 minutes were tested after formalin injection. Spontaneous nocifensive responses were video recorded. Experiment 2 – Complete Freund’s Adjuvant (CFA)-induced arthritis. CFA was injected into the ankle joint of rats. Joint compression thresholds (JCT) were measured. CAV1001 was compared to celecoxib. Experiment 3 – Spinal nerve ligation (SNL) in rats. Paw compression thresholds (PCT) were measured. CAV1001 was compared to gabapentin. Experiment 4 – MMRT-1 bone cancer implantation into the rat tibia. Weight-bearing was assessed. CAV1001 was compared to morphine.

Results

In Phase 2 of the formalin model, CAV1001 (1 mg/kg) significantly reduced pain behaviors to a degree comparable to the peripherally restricted kappa-opioid agonist, ICI204448 (10 mg/kg). CAV1001 (10 mg/kg) effectively eliminated pain behaviors associated with phase 2. In the CFA-induced arthritis model, a significant increase in JCTs, similar to the comparator celecoxib, was observed with CAV1001 at 1 mg/kg at 2 hours; CAV1001 (10 mg/kg) was effective at 1 hour. In the SNL model, both the comparator gabapentin and CAV1001 (5 mg/kg) significantly reduced PCT at 2 hours, but at 4 hours, the CAV1001 thresholds improved to baseline. CAV1001 10 mg/kg significantly improved weight bearing at 4-hour post-dosing compared to baseline following MMRT-1 implantation.

Conclusion

CAV1001 demonstrated efficacy in several different preclinical pain models. Time- and dose-dependent differences in the efficacy of CAV1001 amongst these rodent pain models parallel the degree of underlying inflammation.

Opioid Use in Fibromyalgia: A Cautionary Tale

Multiple pharmacotherapies are available for the treatment of fibromyalgia (FM), including opioid analgesics. We postulate that the mechanism of action of traditional opioids predicts their lack of efficacy in FM. Literature searches of the MEDLINE and Cochrane Library databases were conducted using the search term opioid AND fibromyalgia to identify relevant articles, with no date limitations set. Citation lists in returned articles and personal archives of references were also examined for additional relevant items, and articles were selected based on the expert opinions of the authors. We found no evidence from clinical trials that opioids are effective for the treatment of FM. Observational studies have found that patients with FM receiving opioids have poorer outcomes than patients receiving nonopioids, and FM guidelines recommend against the use of opioid analgesics. Despite this, and despite the availability of alternative Food and Drug Administration-approved pharmacotherapies and the efficacy of nonpharmacologic therapies, opioids are commonly used in the treatment of FM. Factors associated with opioid use include female sex; geographic variation; psychological factors; a history of opioid use, misuse, or abuse; and patient or physician preference. The long-term use of opioid analgesics is of particular concern in the United States given the ongoing public health emergency relating to excess prescription opioid consumption. The continued use of opioids to treat FM despite a proven lack of efficacy, lack of support from treatment guidelines, and the availability of approved pharmacotherapy options provides a cautionary tale for their use in other chronic pain conditions.

Comparing Genomic Profiles of Women With and Without Fibromyalgia

BACKGROUND

Fibromyalgia syndrome (FMS), a chronic musculoskeletal condition characterized by diffuse pain, fatigue, sleep impairment, and cognitive dysfunction, is associated with significant functional disability. Its underlying biological mechanisms are unknown. This study investigated differentially expressed genes between women with FMS and healthy volunteers.

METHODS

Women who met the 1990 or 2010 American College of Rheumatology fibromyalgia criteria were compared to age- and race-matched pain-free healthy women. Peripheral blood samples were collected, and a full genome microarray gene expression analysis was performed. One-way analysis of variance was used to identify differentially expressed genes using the filtering criterion of 1% false discovery rate. Analysis of canonical pathways associated with these genes was performed. Confirmatory quantitative real-time polymerase chain reaction and enzyme-linked immunosorbent assay verified microarray results. Independent t-tests compared gene and protein expression between groups.

RESULT

Participants were 54 women with FMS and 25 controls. Expression arrays from a subset of women with FMS (n = 29) and controls (n = 20) showed upregulation of 12 genes (>1.8-fold change, p < .05) in the FMS sample. Differentially expressed genes were related to B-cell development, primary immunodeficiency signaling, and mitotic roles of polo-like kinase. CENPK and HSP90AA1 were the most differentially expressed genes (p < .01).

CONCLUSION

Activity of interrelated pathways related to immune response, and homeostasis appears to be relevant to the experience of FMS. Replication and exploration of the relationship between gene expression and symptom severity will help determine clinical relevance of these findings.

Skin cytokine expression in patients with fibromyalgia syndrome is not different from controls

Background

Fibromyalgia syndrome (FMS) is a chronic pain syndrome of unknown etiology. There is increasing evidence for small nerve fiber impairment in a subgroup of patients with FMS. We investigated whether skin cytokine and delta opioid receptor (DOR) gene expression in FMS patients differs from controls as one potential contributor to small nerve fiber sensitization.

Methods

We investigated skin punch biopsies of 25 FMS patients, ten patients with monopolar depression but no pain, and 35 healthy controls. Biopsies were obtained from the lateral upper thigh and lower calf. Gene expression of the pro-inflammatory cytokines tumor necrosis factor-alpha (TNF), interleukin (IL)-6, and IL-8 and of the anti-inflammatory cytokine IL-10 was analyzed using quantitative real-time PCR and normalizing data to 18sRNA as housekeeping gene. Additionally, we assessed DOR gene expression.

Results

All cytokines and DOR were detectable in skin samples of FMS patients, patients with depression, and healthy controls without intergroup difference. Also, gene expression was not different in skin of the upper and lower leg within and between the groups and in FMS patient subgroups.

Conclusions

Skin cytokine and DOR gene expression does not differ between patients with FMS and controls. Our results do not support a role of the investigated cytokines in sensitization of peripheral nerve fibers as a potential mechanism of small fiber pathology in FMS.

Dermatologic manifestations of fibromyalgia

The aim of this study was to determine the common dermatologic diagnoses and skin-related symptoms in a cohort of patients with fibromyalgia seen in a tertiary referral center. A retrospective chart review was performed of all patients with a fibromyalgia diagnosis from January 1 to December 31, 2008, whose diagnosis was confirmed in the Fibromyalgia and Chronic Fatigue Clinic at Mayo Clinic in Rochester, Minnesota. Charts were reviewed for dermatologic conditions and cutaneous symptoms. Demographic and clinical data were collected to assess the frequency of skin-related issues in patients with fibromyalgia. Of 2,233 patients screened, 845 patients met the inclusion criteria of having a confirmed diagnosis of fibromyalgia. Among these fibromyalgia patients, various dermatologic conditions and cutaneous problems were identified, including hyperhidrosis in 270 (32.0 %), burning sensation of the skin or mucous membranes in 29 (3.4 %), and various unusual cutaneous sensations in 14 (1.7 %). Pruritus without identified cause was noted by 28 patients (3.3 %), with another 16 patients (1.9 %) reporting neurotic excoriations, prurigo nodules, or lichen simplex chronicus. Some form of dermatitis other than neurodermatitis was found in 77 patients (9.1 %). Patients with fibromyalgia may have skin-related symptoms associated with their fibromyalgia. No single dermatologic diagnosis appears to be overrepresented in this population, with the exception of a subjective increase in sweating.

Pharmacological traits of delta opioid receptors: pitfalls or opportunities?

RATIONALE

Delta opioid receptors (DORs) have been considered as a potential target to relieve pain as well as treat depression and anxiety disorders and are known to modulate other physiological responses, including ethanol and food consumption. A small number of DOR-selective drugs are in clinical trials, but no DOR-selective drugs have been approved by the Federal Drug Administration and some candidates have failed in phase II clinical trials, highlighting current difficulties producing effective delta opioid-based therapies. Recent studies have provided new insights into the pharmacology of the DOR, which is often complex and at times paradoxical.

OBJECTIVE

This review will discuss the existing literature focusing on four aspects: (1) Two DOR subtypes have been postulated based on differences in pharmacological effects of existing DOR-selective ligands. (2) DORs are expressed ubiquitously throughout the body and central nervous system and are, thus, positioned to play a role in a multitude of diseases. (3) DOR expression is often dynamic, with many reports of increased expression during exposure to chronic stimuli, such as stress, inflammation, neuropathy, morphine, or changes in endogenous opioid tone. (4) A large structural variety in DOR ligands implies potential different mechanisms of activating the receptor.

CONCLUSION

The reviewed features of DOR pharmacology illustrate the potential benefit of designing tailored or biased DOR ligands.

Delta opioid receptor analgesia: recent contributions from pharmacology and molecular approaches

Delta opioid receptors represent a promising target for the development of novel analgesics. A number of tools have been developed recently that have significantly improved our knowledge of δ receptor function in pain control. These include several novel δ agonists with potent analgesic properties, and genetic mouse models with targeted mutations in the δ opioid receptor gene. Also, recent findings have further documented the regulation of δ receptor function at cellular level, which impacts on the pain-reducing activity of the receptor. These regulatory mechanisms occur at transcriptional and post-translational levels, along agonist-induced receptor activation, signaling and trafficking, or in interaction with other receptors and neuromodulatory systems. All these tools for in-vivo research, and proposed mechanisms at molecular level, have tremendously increased our understanding of δ receptor physiology, and contribute to designing innovative strategies for the treatment of chronic pain and other diseases such as mood disorders.

Dysfunctional neurotransmitter systems in fibromyalgia, their role in central stress circuitry and pharmacological actions on these systems

Fibromyalgia is considered a stress-related disorder, and hypo- as well as hyperactive stress systems (sympathetic nervous system and hypothalamic-pituitary-adrenal axis) have been found. Some observations raise doubts on the view that alterations in these stress systems are solely responsible for fibromyalgia symptoms. Cumulative evidence points at dysfunctional transmitter systems that may underlie the major symptoms of the condition. In addition, all transmitter systems found to be altered in fibromyalgia influence the body's stress systems. Since both transmitter and stress systems change during chronic stress, it is conceivable that both systems change in parallel, interact, and contribute to the phenotype of fibromyalgia. As we outline in this paper, subgroups of patients might exhibit varying degrees and types of transmitter dysfunction, explaining differences in symptomatoloy and contributing to the heterogeneity of fibromyalgia. The finding that not all fibromyalgia patients respond to the same medications, targeting dysfunctional transmitter systems, further supports this hypothesis.

Genetics and Gene Expression Involving Stress and Distress Pathways in Fibromyalgia with and without Comorbid Chronic Fatigue Syndrome

In complex multisymptom disorders like fibromyalgia syndrome (FMS) and chronic fatigue syndrome (CFS) that are defined primarily by subjective symptoms, genetic and gene expression profiles can provide very useful objective information. This paper summarizes research on genes that may be linked to increased susceptibility in developing and maintaining these disorders, and research on resting and stressor-evoked changes in leukocyte gene expression, highlighting physiological pathways linked to stress and distress. These include the adrenergic nervous system, the hypothalamic-pituitary-adrenal axis and serotonergic pathways, and exercise responsive metabolite-detecting ion channels. The findings to date provide some support for both inherited susceptibility and/or physiological dysregulation in all three systems, particularly for catechol-O-methyl transferase (COMT) genes, the glucocorticoid and the related mineralocorticoid receptors (NR3C1, NR3C2), and the purinergic 2X4 (P2X4) ion channel involved as a sensory receptor for muscle pain and fatigue and also in upregulation of spinal microglia in chronic pain models. Methodological concerns for future research, including potential influences of comorbid clinical depression and antidepressants and other medications, on gene expression are also addressed.