Activational action of testosterone on androgen receptors protects males preventing temporomandibular joint pain

Metabolic profiling of synovial fluid in human temporomandibular joint osteoarthritis

Introduction

Temporomandibular joint (TMJ) osteoarthritis (OA) is a common TMJ degenerative disease with an unclear mechanism. Synovial fluid (SF), an important component of TMJ, contains various proteins and metabolites that may directly contribute to OA. The present study aimed to investigate the influence of SF in TMJOA at the metabolite level.

Methods

Untargeted and widely targeted metabolic profiling were employed to identify metabolic changes in SF of 90 patients with different TMJOA grades according to TMJ magnetic resonance imaging.

Results

A total 1498 metabolites were detected. Most of the metabolites were amino acids and associated metabolites, benzene and substituted derivatives, and lipids. Among patients with mild, moderate and severe TMJOA, 164 gradually increasing and 176 gradually decreasing metabolites were identified, indicating that biosynthesis of cofactors, choline metabolism, mineral absorption and selenocompound metabolism are closely related to TMJOA grade. Combined metabolomics and clinical examination revealed 37 upregulated metabolites and 16 downregulated metabolites in patients with pain, of which 19 and 26 metabolites were positively and negatively correlated, respectively, with maximum interincisal opening. A model was constructed to diagnose TMJOA grade and nine biomarkers were identified. The identified metabolites are key to exploring the mechanism of TMJOA.

Discussion

In the present study, a metabolic profile was constructed and assessed using a much larger number of human SF samples from patients with TMJOA, and a model was established to contribute to the diagnosis of TMJOA grade. The findings expand our knowledge of metabolites in human SF of TMJOA patients, and provide an important basis for further research on the pathogenesis and treatment of TMJOA.

Impact of continuous testosterone exposure on reproductive physiology, activity, and pain-related behavior in young adult female rats

Testosterone may reduce pain in cisgender women and transgender men. Rodents can provide a useful model for investigating physiological effects of hormone therapy. To this end, continuous-release testosterone or blank (placebo) capsules were implanted s.c. into young adult female rats, and three weeks later rats were either ovariectomized or sham-ovariectomized. Testosterone treatment that mimicked previously reported endogenous levels in males eliminated estrous cycling and decreased uterine weight. Testosterone also significantly increased body weight and suppressed the increases in daily wheel running observed in placebo controls over time. Subsequent ovariectomy or sham-ovariectomy decreased wheel running in all groups, but testosterone-treated rats recovered significantly more quickly than did placebo-treated rats. Neither testosterone nor ovariectomy significantly altered hindpaw mechanical threshold. Two weeks after sham/ovariectomy surgery, injection of Complete Freund Adjuvant (CFA) into one hindpaw reduced wheel running and mechanical threshold in all groups; running significantly decreased from the first to second day after CFA in testosterone- but not in placebo-treated rats. Morphine 1.0 but not 3.2 mg/kg increased CFA-suppressed wheel running similarly in all groups, whereas both doses of morphine increased CFA-suppressed mechanical threshold. These data suggest that weeks-long testosterone treatment with or without ovariectomy may provide a useful physiological model of testosterone therapy as used in human gender transition. Although testosterone administered at levels similar to those in gonadally intact males tended to hasten female rats' recovery from surgery, it did not decrease maximal pain-related behaviors after surgery or hindpaw inflammatory insult, nor did it alter opioid antinociception.

Sex as a Biological Variable in Oral Diseases: Evidence and Future Prospects

The interest of the scientific community on sex and gender differences in health and disease has increased substantially over the past 25 to 30 y as a result of a long process of events and policies in the biomedical field. This is crucial as compelling evidence from human and animal model studies has demonstrated that sex and gender influence health, molecular and cellular processes, and response and predisposition to disease. The present scoping review aims to provide a synthesis of sex differences in oral diseases, ranging from periodontal disease to orofacial pain conditions, from risk of caries development to apical periodontitis. Overall, findings from this review further support a role for sexual dimorphism influencing disease predisposition and/or progression in oral diseases. Of note, this review also highlights the lack of consideration of additional factors such as gender and other psychosocial and external factors potentially influencing oral health and disease. New conceptual frameworks capable of capturing multiple fundamental domains and measurements should be developed in clinical and preclinical studies to inform sex-based individualized preventive and treatment strategies.

Interleukin-10-producing monocytes contribute to sex differences in pain resolution in mice and humans

Pain is closely associated with the immune system, which exhibits sexual dimorphism. For these reasons, neuro-immune interactions are suggested to drive sex differences in pain pathophysiology. However, our understanding of peripheral neuro-immune interactions on sex differences in pain resolution remains limited. Here, we have shown, in both a mouse model of inflammatory pain and in humans following traumatic pain, that males had higher levels of interleukin (IL)-10 than females, which were correlated with faster pain resolution. Following injury, we identified monocytes (CD11b+ Ly6C+ Ly6G-F4/80 mid ) as the primary source of IL-10, with IL-10-producing monocytes being more abundant in males than females. In a mouse model, neutralizing IL-10 signaling through antibodies, genetically ablating IL-10R1 in sensory neurons, or depleting monocytes with clodronate all impaired the resolution of pain hypersensitivity in both sexes. Furthermore, manipulating androgen levels in mice reversed the sexual dimorphism of pain resolution and the levels of IL-10-producing monocytes. These results highlight a novel role for androgen-driven peripheral IL-10-producing monocytes in the sexual dimorphism of pain resolution. These findings add to the growing concept that immune cells play a critical role in resolving pain and preventing the transition into chronic pain.

Graphical abstract

Selective androgen receptor modulator microparticle formulation reverses muscle hyperalgesia in a mouse model of widespread muscle pain

ABSTRACT

Chronic pain is a significant health problem associated with disability and reduced quality of life. Current management of chronic pain is inadequate with only modest effects of pharmacological interventions. Thus, there is a need for the generation of analgesics for treating chronic pain. Although preclinical and clinical studies demonstrate the analgesic effects of testosterone, clinical use of testosterone is limited by adverse androgenic effects. Selective androgen receptor modulators (SARMs) activate androgen receptors and overcome treatment limitations by minimizing androgenic side effects. Thus, we tested whether daily soluble SARMs or a SARM-loaded microparticle formulation alleviated muscle hyperalgesia in a mouse-model of widespread pain (male and female C57BL/6J mice). We tested whether the analgesic effects of the SARM-loaded microparticle formulation was mediated through androgen receptors by blocking androgen receptors with flutamide pellets. In vitro and in vivo release kinetics were determined for SARM-loaded microparticles. Safety and toxicity of SARM treatment was determined using serum cardiac and liver toxicity panels, heart histology, and conditioned place preference testing. Subcutaneous daily SARM administration, and 2 injections, 1 week apart, of SARM-loaded microparticles alleviated muscle hyperalgesia in both sexes and was prevented with flutamide treatment. Sustained release of SARM, from the microparticle formulation, was observed both in vitro and in vivo for 4 weeks. Selective androgen receptor modulator treatment produced no cardiac or liver toxicity and did not produce rewarding behaviors. These studies demonstrate that SARM-loaded microparticles, which release drug for a sustained period, alleviate muscle pain, are safe, and may serve as a potential therapeutic for chronic muscle pain.

Association of temporomandibular joint osteoarthrosis with dentoskeletal morphology in males: A cone-beam computed tomography and cephalometric analysis

OBJECTIVE

The objective of the study was to assess the differences in dentoskeletal morphology in males with and without temporomandibular joint osteoarthrosis (TMJOA).

METHODS

Three hundred seventy-one male participants seeking orthodontic treatment were enrolled in this cross-sectional study. Each participant's osseous status was evaluated using cone-beam computed tomography (CBCT) and classified into normal (N = 104), indeterminate for TMJOA (N = 110) and TMJOA (N = 157) groups. The dentoskeletal characteristics were evaluated using cephalograms. Stratified analysis was performed based on age and skeletal pattern. Descriptive statistics and one-way analysis of variance were performed to investigate dentoskeletal differences among groups. P < .05 was considered statistically significant.

RESULTS

The differences in posterior cranial base length, FMA, MP-OP, anterior facial height, articular angle, ramus height and L1-MP were statistically significant. After stratification by age, the differences in FMA, maxillomandibular angle, posterior facial height, facial height ratio, gonial angle and mandibular body length were statistically significant in adults. No statistical difference except for articular angle was observed in adolescents. After stratification by skeletal pattern, statistical differences were mainly apparent in skeletal Class II adults.

CONCLUSION

Males with TMJOA showed a posteriorly positioned and backward-rotated mandible, especially in skeletal Class II adults. Compared with women, the craniofacial morphology of men is less affected by TMJOA. The association between TMJOA and craniofacial morphology also varied across different age groups and skeletal patterns. Prospective studies are required to clarify the cause-effect relationship between TMJOA and craniofacial morphology in males.

Resistance training protects against muscle pain through activation of androgen receptors in male and female mice

ABSTRACT

Resistance training-based exercise is commonly prescribed in the clinic for the treatment of chronic pain. Mechanisms of aerobic exercise for analgesia are frequently studied, while little is known regarding resistance training mechanisms. We developed a resistance training model in mice and hypothesized resistance training would protect against development of muscle pain, mediated through the activation of androgen receptors. Activity-induced muscle hyperalgesia was produced by 2 injections of pH 5.0 stimuli with fatiguing muscle contractions. Resistance training was performed by having mice climb a ladder with attached weights, 3 times per week. Resistance training acutely increased blood lactate and prolonged training increased strength measured via forepaw grip strength and 1 repetition maximum, validating the exercise program as a resistance training model. Eight weeks of resistance training prior to induction of the pain model blocked the development of muscle hyperalgesia in both sexes. Resistance training initiated after induction of the pain model reversed muscle hyperalgesia in male mice only. A single resistance training bout acutely increased testosterone in male but not female mice. Administration of the androgen receptor antagonist flutamide (200 mg pellets) throughout the 8-week training program blocked the exercise-induced protection against muscle pain in both sexes. However, single administration of flutamide (1, 3, 10 mg/kg) in resistance-trained animals had no effect on existing exercise-induced protection against muscle pain. Therefore, resistance training acutely increases lactate and testosterone and strength overtime. Eight weeks of resistance training prevents the development of hyperalgesia through the activation of androgen receptors in an animal model of muscle pain.

"Testosterone decreases temporomandibular joint nociception"- A systematic review of studies on animal models

OBJECTIVE

The aim of the present systematic review was to assess the effect of testosterone on temporomandibular joint (TMJ) nociception.

DESIGN

A systematic review of pertinent indexed literature was performed. The focused question addressed was "Is there a connection between testosterone and TMJ nociception?" Original studies were included. In-vitro and ex-vivo studies, case-reports/series, letters to the Editor and commentaries were not sought. Indexed databases were searched without time and language restrictions up to and including September 2021 using different free text key words: testosterone OR "male sex hormones" OR "gonadal hormones" AND "temporomandibular joint" OR "temporomandibular dysfunction" AND nociception AND males. The literature search was performed in accordance with the preferred reporting outcomes of systematic reviews and meta-analysis guidelines. The risk of bias (RoB) was assessed using the SYstematic Review Centre for Laboratory animal Experimentation (SYRCLE) tool.

RESULTS

Out of the 406 studies identified, seven studies on animal-models were included. All studies were performed in rats with age and weight ranging between 21 and 90 days and 200-300 g, respectively. Testosterone was administered in concentrations ranging between 1 and 10 mg/Kg. Results from all studies showed that testosterone administration in gonadectomized male rats reduces induced TMJ nociception. The RoB was high in 3 and unclear in 4 studies.

CONCLUSION

Testosterone offers protection against TMJ nociception in male rats; however, from a clinical perspective, potential contribution of testosterone therapy towards the management of TMD remains indeterminate.

Cannabidiol has therapeutic potential for myofascial pain in female and male parkinsonian rats

The musculoskeletal orofacial pain is a complex symptom of Parkinson's disease (PD) resulting in stomatognathic system dysfunctions aggravated by the disease rigidity and postural instability. We tested the effect of cannabidiol (CBD), a non-psychotomimetic constituent of Cannabis sativa, in PD-related myofascial pain. Wistar adult female and male rats orofacial allodynic and hyperalgesic responses were tested by Von Frey and formalin tests, before and 21 days past 6-OHDA lesion. Algesic response was tested after masseter muscle injection of CBD (10, 50, 100 μg in 10 μL) or vehicle. Males compared to females in all estrous cycles' phases presented reduced orofacial allodynia and hyperalgesia. According to the estrous cycle's phases, females presented distinct orofacial nociceptive responses, being the estrus phase well-chosen for nociceptive analysis after 6-OHDA lesion (phase with fewer hormone alterations and adequate length). Dopaminergic neuron lesion decreased mechanical and inflammatory nociceptive thresholds in females and males in a higher proportion in females. CBD local treatment reduced the increased orofacial allodynia and hyperalgesia, in males and females. The female rats were more sensitive to CBD effect considering allodynia, responding to the lowest dose. Although females and males respond to the effect of three doses of CBD in the formalin test, males showed a superior reduction in the hyperalgesic response. These results indicate that hemiparkinsonian female in the estrus phase and male answer differently to the different doses of CBD therapy and nociceptive tests. CBD therapy is effective for parkinsonism-induced orofacial nociception.

Testosterone protects against the development of widespread muscle pain in mice

Chronic widespread pain conditions are more prevalent in women than men, suggesting a role for gonadal hormones in the observed differences. Previously, we showed that female mice, compared to male, develop widespread, more severe, and longer-duration hyperalgesia in a model of activity-induced muscle pain. We hypothesized testosterone protects males from developing the female pain phenotype. We tested whether orchiectomy of males before induction of an activity-induced pain model produced a female phenotype and whether testosterone administration produced a male phenotype in females. Orchiectomy produced longer-lasting, more widespread hyperalgesia, similar to females. Administration of testosterone to females or orchiectomized males produced unilateral, shorter-lasting hyperalgesia. Prior studies show that the serotonin transporter (SERT) is increased in the nucleus raphe magnus (NRM) in models of chronic pain, and that blockade of SERT in the NRM reduces hyperalgesia. We examined potential sex differences in the distribution of SERT across brain sites involved in nociceptive processing using immunohistochemistry. A sex difference in SERT was found in the NRM in the activity-induced pain model; females had greater SERT immunoreactivity than males. This suggests that testosterone protects against development of widespread, long-lasting muscle pain and that alterations in SERT may underlie the sex differences.

Increased expression of dendrin in the dorsal horn of the spinal cord during stress is regulated by sex hormones

Chronic stress has various effects on organisms and is sex-specific. The aim of the study was to describe the expression of synapse strengthening protein, dendrin, in the spinal cord (SC) and the dependence of its expression on chronic stress and sex hormones. Thirteen-month-old female and male rats were castrated (ovariectomy [F-OVX] or orchidectomy [M-ORX]) or sham-operated (F-SH or M-SH), respectively. At age 15 months, three 10-day-sessions of sham stress (control, C) or chronic stress (S) were conducted. Dendrin expression was present in the thoracic SC segments and the dorsal root ganglia (DRG). In the SC, dendrin expression was prominent in superficial laminae of the dorsal horn and lamina X (central canal). The M-ORX-S group had the highest dendrin expression in the dorsal horn, being significantly higher than the M-ORX-C or M-SH-S groups (P < 0.05). Dendrin expression was significantly higher in the F-SH-S group than the F-SH-C group (P < 0.05), as well as in the F-SH-S than the M-SH-S (P < 0.05). Co-localization with the α-d-galactosyl-specific isolectin B4 (IB4) in central projections of the DRG neurons in the dorsal horn of the SC was 7.43 ± 3.36%, while with the calcitonin gene-related peptide (CGRP) was 8.47 ± 4.45%. Localization of dendrin was observed in soma and nuclei of neurons in the dorsal horn. Dendrin expression in pain-processing areas of the SC, the DRG neurons and their peripheral projections suggest possible roles in pain perception and modulation. Stress-induced increase in dendrin expression and its dependence on sex hormones may partially explain sex-specific pain hypersensitivity induced by stress.

Sexual Dimorphism in the Expression of Pain Phenotype in Preclinical Models of Rheumatoid Arthritis

Rheumatoid arthritis is one of most frequent rheumatic diseases, affecting around 1% of the population worldwide. Pain impacting the quality of life for the patient with rheumatoid arthritis, is often the primary factor leading them to seek medical care. Although sex-related differences in humans and animal models of rheumatoid arthritis are described, the correlation between pain and sex in rheumatoid arthritis has only recently been directly examined. Here we review the literature and explore the mechanisms underlying the expression of the pain phenotype in females and males in preclinical models of rheumatoid arthritis.

Influence of androgenic blockade with flutamide on pain behaviour and expression of the genes that encode the NaV1.7 and NaV1.8 voltage-dependent sodium channels in a rat model of postoperative pain

Background

Experimental studies suggest that testosterone reduces the nociceptive response after inflammatory and neuropathic stimuli, however the underlying mechanisms have not been fully elucidated. The aims of this study were to evaluate the effect of peripheral blockade of testosterone on pain behaviour and on expression levels of the genes that encode the NaV1.7 and NaV1.8 channels, in dorsal root ganglia in an acute postoperative pain model, as well as the influence of androgen blockade on the expression of these genes.

Methods

Postoperative pain was induced by a plantar incision and the study group received flutamide to block testosterone receptor. The animals were submitted to behavioural evaluation preoperatively, 2 h after incision, and on the 1st, 2nd, 3rd and 7th postoperative days. Von Frey test was used to evaluate paw withdrawal threshold after mechanical stimuli and the guarding pain test to assess spontaneous pain. The expression of the genes encoding the sodium channels at the dorsal root ganglia was determined by real time quantitative polymerase chain reaction.

Results

Animals treated with flutamide presented lower paw withdrawal threshold at the 1st, 2nd, 3rd, and 7th postoperative days. The guarding pain test showed significant decrease in the flutamide group at 2 h and on the 3rd and 7th postoperative days. No difference was detected between the study and control groups for the gene expression.

Conclusions

Our data suggest an antinociceptive effect of androgens following plantar incision. The expression of genes that encode voltage-gated sodium channels was not influenced by androgen blockade.

Differences Between the Prenatal Effects of Fluoxetine or Buspirone Alone or in Combination on Pain and Affective Behaviors in Prenatally Stressed Male and Female Rats

The selective serotonin reuptake inhibitor fluoxetine and the 5-HT1A receptor agonist buspirone are used to treat depression and anxiety. Previously we demonstrated that chronic stress during pregnancy (prenatal stress) in rats, used as a model of maternal depression risk, increased inflammatory pain and depressive-like behavior in the offspring; buspirone injected to pregnant dams was protective. Clinically, the addition of buspirone to fluoxetine increases the latter’s efficacy in treating depression in patients. Here, we investigated the influence of repeated prenatal injections of fluoxetine, buspirone or their combination on pain- and depressive-like behaviors in prenatally stressed young male and female rats. Prenatal stress augmented depressive-like behavior and both thermal and inflammatory pain (formalin test), replicating our prior findings, and increased basal levels of corticosterone in the blood plasma. Both drugs and their combination reduced the effects of prenatal stress on thermal pain and depressive-like behavior independently of sex. The combination of fluoxetine and buspirone, compared with fluoxetine, was more antinociceptive in the hot plate test in both sexes, and when compared with buspirone, was more antinociceptive only in males. A detailed study of the time-course of formalin-induced pain showed a nuanced effect of these drugs that was sex-dependent. The combination of the two drugs was less effective in females than males during the initial acute phase of nociceptive behavior in flexing + shaking behaviors, whereas that combination was more effective than fluoxetine alone in the first acute phase of licking behavior in females. The antinociceptive effect of buspirone dominated that of the drug combination and of fluoxetine alone, especially during the interphase of the formalin test in both sexes for both flexing + shaking and licking, suggesting a more effective prenatal action of buspirone on the development of a descending serotonergic inhibitory system modulating pain in the spinal cord dorsal horn neurons. Our results indicate that inflammatory pain-like responses integrated at the spinal level in males were more vulnerable to prenatal stress than females. In licking, the antinociceptive effect of fluoxetine and drug combination in the interphase was more in males than females. The data underscore the importance of considering sexual dimorphism when using drug therapy.

TRP Channels as Potential Targets for Sex-Related Differences in Migraine Pain

Chronic pain is one of the most debilitating human diseases and represents a social and economic burden for our society. Great efforts are being made to understand the molecular and cellular mechanisms underlying the pathophysiology of pain transduction. It is particularly noteworthy that some types of chronic pain, such as migraine, display a remarkable sex dimorphism, being up to three times more prevalent in women than in men. This gender prevalence in migraine appears to be related to sex differences arising from both gonadal and genetic factors. Indeed, the functionality of the somatosensory, immune, and endothelial systems seems modulated by sex hormones, as well as by X-linked genes differentially expressed during development. Here, we review the current data on the modulation of the somatosensory system functionality by gonadal hormones. Although this is still an area that requires intense investigation, there is evidence suggesting a direct regulation of nociceptor activity by sex hormones at the transcriptional, translational, and functional levels. Data are being accumulated on the effect of sex hormones on TRP channels such as TRPV1 that make pivotal contributions to nociceptor excitability and sensitization in migraine and other chronic pain syndromes. These data suggest that modulation of TRP channels' expression and/or activity by gonadal hormones provide novel pathways for drug intervention that may be useful for targeting the sex dimorphism observed in migraine.

Opposing Roles of Estradiol and Testosterone on Stress-Induced Visceral Hypersensitivity in Rats

Chronic stress produces maladaptive pain responses, manifested as alterations in pain processing and exacerbation of chronic pain conditions including irritable bowel syndrome. Female predominance, especially during reproductive years, strongly suggests a role of gonadal hormones. However, gonadal hormone modulation of stress-induced pain hypersensitivity is not well understood. In the present study, we tested the hypothesis that estradiol is pronociceptive and testosterone is antinociceptive in a model of stress-induced visceral hypersensitivity (SIVH) in rats by recording the visceromotor response to colorectal distention after a 3-day forced swim (FS) stress paradigm. FS induced visceral hypersensitivity that persisted at least 2 weeks in female, but only 2 days in male rats. Ovariectomy blocked and orchiectomy facilitated SIVH. Furthermore, estradiol injection in intact male rats increased SIVH and testosterone in intact female rats attenuated SIVH. Western blot analyses indicated estradiol increased excitatory glutamate ionotropic receptor NMDA type subunit 1 expression and decreased inhibitory metabotropic glutamate receptor 2 expression after FS in male thoracolumbar spinal cord. In addition, the presence of estradiol during stress increased spinal brain-derived neurotrophic factor (BDNF) expression independent of sex. In contrast, testosterone blocked the stress-induced increase in BDNF expression in female rats. These data suggest that estradiol facilitates and testosterone attenuates SIVH by modulating spinal excitatory and inhibitory glutamatergic receptor expression.

PERSPECTIVE

SIVH is more robust in female rats. Estradiol facilitates whereas testosterone dampens the development of SIVH. This could partially explain the greater prevalence of certain chronic visceral pain conditions in women. An increase in spinal BDNF is concomitant with increased stress-induced pain. Pharmaceutical interventions targeting this molecule could provide promising alleviation of SIVH in women.

Neonatal Handling Produces Sex Hormone-Dependent Resilience to Stress-Induced Muscle Hyperalgesia in Rats

Neonatal handling (NH) of male rat pups strongly attenuates stress response and stress-induced persistent muscle hyperalgesia in adults. Because female sex is a well established risk factor for stress-induced chronic muscle pain, we explored whether NH provides resilience to stress-induced hyperalgesia in adult female rats. Rat pups underwent NH, or standard (control) care. Muscle mechanical nociceptive threshold was assessed before and after water avoidance (WA) stress, when they were adults. In contrast to male rats, NH produced only a modest protection against WA stress-induced muscle hyperalgesia in female rats. Gonadectomy completely abolished NH-induced resilience in male rats but produced only a small increase in this protective effect in female rats. The administration of the antiestrogen drug fulvestrant, in addition to gonadectomy, did not enhance the protective effect of NH in female rats. Finally, knockdown of the androgen receptor by intrathecal antisense treatment attenuated the protective effect of NH in intact male rats. Together, these data indicate that androgens play a key role in NH-induced resilience to WA stress-induced muscle hyperalgesia.

PERSPECTIVE

NH induces androgen-dependent resilience to stress-induced muscle pain. Therefore, androgens may contribute to sex differences observed in chronic musculoskeletal pain and its enhancement by stress.