Needling adenosine receptors for pain relief

Caffeine Impaired Acupuncture Analgesia in Inflammatory Pain by Blocking Adenosine A1 Receptor

Caffeine consumption inhibits acupuncture analgesic effects by blocking adenosine signaling. However, existing evidence remains controversial. Hence, this study aimed to examine the adenosine A1 receptor (A1R) role in moderate-dose caffeine-induced abolishing effect on acupuncture analgesia using A1R knockout mice (A1R-/-). We assessed the role of A1R in physiological sensory perception and its interaction with caffeine by measuring mechanical and thermal pain thresholds and administering A1R and adenosine 2A receptor antagonists in wild-type (WT) and A1R-/- mice. Formalin- and complete Freund's adjuvant (CFA)-induced inflammatory pain models were recruited to explore moderate-dose caffeine effect on pain perception and acupuncture analgesia in WT and A1R-/- mice. Moreover, a C-fiber reflex electromyogram in the biceps femoris was conducted to validate the role of A1R in the caffeine-induced blockade of acupuncture analgesia. We found that A1R was dispensable for physiological sensory perception and formalin- and CFA-induced hypersensitivity. However, genetic deletion of A1R impaired the antinociceptive effect of acupuncture in A1R-/- mice under physiological or inflammatory pain conditions. Acute moderate-dose caffeine administration induced mechanical and thermal hyperalgesia under physiological conditions but not in formalin- and CFA-induced inflammatory pain. Moreover, caffeine significantly inhibited electroacupuncture (EA) analgesia in physiological and inflammatory pain in WT mice, comparable to that of A1R antagonists. Conversely, A1R deletion impaired the EA analgesic effect and decreased the caffeine-induced inhibitory effect on EA analgesia in physiological conditions and inflammatory pain. Moderate-dose caffeine administration diminished the EA-induced antinociceptive effect by blocking A1R. Overall, our study suggested that caffeine consumption should be avoided during acupuncture treatment. PERSPECTIVE: Moderate-dose caffeine injection attenuated EA-induced antinociceptive effect in formalin- and CFA-induced inflammatory pain mice models by blocking A1R. This highlights the importance of monitoring caffeine intake during acupuncture treatment.

The role of purinergic signaling in acupuncture-mediated relief of neuropathic and inflammatory pain

Acupuncture is a traditional medicinal practice in China that has been increasingly recognized in other countries in recent decades. Notably, several reports have demonstrated that acupuncture can effectively aid in pain management. However, the analgesic mechanisms through which acupuncture provides such benefits remain poorly understood. Purinergic signaling, which is mediated by purine nucleotides and purinergic receptors, has been proposed to play a central role in acupuncture analgesia. On the one hand, acupuncture affects the transmission of nociception by increasing adenosine triphosphate dephosphorylation and thereby decreasing downstream P2X3, P2X4, and P2X7 receptors signaling activity, regulating the levels of inflammatory factors, neurotrophic factors, and synapsin I. On the other hand, acupuncture exerts analgesic effects by promoting the production of adenosine, enhancing the expression of downstream adenosine A1 and A2A receptors, and regulating downstream inflammatory factors or synaptic plasticity. Together, this systematic overview of the field provides a sound, evidence-based foundation for future research focused on the application of acupuncture as a means of relieving pain.

Leishmania mexicana promotes pain-reducing metabolomic reprogramming in cutaneous lesions

Cutaneous leishmaniasis (CL) is characterized by extensive skin lesions, which are usually painless despite being associated with extensive inflammation. The molecular mechanisms responsible for this analgesia have not been identified. Through untargeted metabolomics, we found enriched anti-nociceptive metabolic pathways in L. mexicana-infected mice. Purines were elevated in infected macrophages and at the lesion site during chronic infection. These purines have anti-inflammatory and analgesic properties by acting through adenosine receptors, inhibiting TRPV1 channels, and promoting IL-10 production. We also found arachidonic acid (AA) metabolism enriched in the ear lesions compared to the non-infected controls. AA is a metabolite of anandamide (AEA) and 2-arachidonoylglycerol (2-AG). These endocannabinoids act on cannabinoid receptors 1 and 2 and TRPV1 channels to exert anti-inflammatory and analgesic effects. Our study provides evidence of metabolic pathways upregulated during L. mexicana infection that may mediate anti-nociceptive effects experienced by CL patients and identifies macrophages as a source of these metabolites.

Acupuncture alleviates acute peritonitis: A case report

Many inflammatory and infectious entities can affect the peritoneum acutely, and patients with peritonitis often have painful expressions. Abdominal pain can be aggravated by coughing, breathing, and turning the body. Here we report the case of an 88-year-old patient with acute gastrointestinal perforation. The patient has been experiencing pain in the right lower abdomen, presenting persistent colic. The X-ray of abdomen and abdominal computed tomography showed perforation of digestive tract. In addition to the use of anti-infection and stomach protection agents, we use different analgesic injections, but the effect on reducing the pain was not obvious. After acupuncture treatment, the patient quickly relieved the pain of acute peritonitis in 1 minute. However, to our knowledge, there is few literature showing that acupuncture relieves preoperative opioid-induced hyperalgesia in patients with acute peritonitis. Based on this case, we suggest acupuncture as an option in the management of relieving the pain of acute peritonitis when opioid therapy is ineffective.

The Effects of Frequent Coffee Drinking on Female-Dominated Healthcare Workers Experiencing Musculoskeletal Pain and a Lack of Sleep

Previous research has demonstrated that chronic diseases can occur due to musculoskeletal (MS) pain and poor sleep. It is also worth noting that the caffeine in coffee can reduce overall sleep duration, efficiency, and quality. Thus, the present study examines the effects of frequent coffee drinking (two cups per day) on individuals experiencing MS pain and a lack of sleep during the COVID-19 period. This observational and cross-sectional study recruited 1615 individuals who completed the self-reported (Nordic musculoskeletal) questionnaire. Long-term, frequent coffee drinking and a sleep duration of less than 6 h per day were significantly associated with neck and shoulder pain among healthy individuals. The mediation model demonstrated that the shorter sleep duration and drinking multiple cups of coffee per day had a two-way relationship that worsened such pain over the long term. Specifically, individuals who experienced such pain frequently drank multiple cups of coffee per day, which, in turn, shortened their sleep durations. In summary, long-term coffee drinking creates a vicious cycle between MS pain and sleep duration. Therefore, the amount of coffee should be fewer than two cups per day for individuals who sleep less than 6 h per day or suffer from MS pain, especially neck and shoulder pain.

The effectiveness and safety of acupuncture treatment on sciatica: A systematic review and meta-analysis

BACKGROUND

Sciatica results from primary or secondary damage to the sciatic nerve in the lumbar or gluteal region. The first option for sciatica is analgesics, but their therapeutic effect and safety in long-term use are questionable. On the other hand, acupuncture has recently been recognized as a complementary and alternative medicine (CAM) to conventional medicine, and studies on its effectiveness and safety have been actively conducted.

OBJECTIVE

To systematically compare acupuncture with analgesics in terms of effect, safety, and durability in the treatment of sciatica METHODS: This review was performed in accordance with Cochrane Handbook for Systematic Reviews of Interventions Version 6.2. Four databases were searched for this review: Wangfang, the Korean Traditional Knowledge Portal (KTKP), PubMed, and EBSCOhost. The primary outcome measures in the review were total effective rate (TER), visual analog scale (VAS) score and pain threshold, and the secondary ones were adverse effects (AEs) and relapse rates. Risk ratio (RR) for TER and mean difference (MD) for VAS score and pain threshold were used as statistics for the meta-analysis of effectiveness, along with associated 95 % confidence intervals (CIs) and P-values. AEs and relapse rates were used for the safety and durability of the interventions. Version 2 of the Cochrane risk-of-bias assessment tool for randomized trials (RoB 2) was used for the methodological quality of randomized controlled trials (RCTs) included in the review.

RESULTS

The synthesized TER of 28 RCTs involving 2707 participants was significantly higher in the acupuncture group compared to the analgesic group (RR [95 % CI] = 1.20 [1.16, 1.24], P < 0.001). The synthesized VAS score of 7 RCTs involving 589 participants was significantly reduced in the acupuncture group compared to the analgesic group (MD [95 % CI] = - 1.78 [- 2.44, - 1.12], P < 0.001). In 5 RCTs involving 311 participants, the synthesized pain threshold was significantly elevated in the acupuncture group compared to the analgesic group (MD [95 % CI] = 0.93 [0.64, 1.22], P < 0.001). Additionally, adverse effects (AEs) and relapse rates of RCTs in the review were lower in the acupuncture group compared to the analgesic group.

CONCLUSION

In this systematic review, acupuncture treatment was significantly effective and safe compared to analgesics in sciatica. In the future, studies with a rigorous study design are required to increase the validity of the effectiveness and safety of acupuncture treatment for sciatica.

A1 Adenosine Receptor Activation Inhibits P2X3 Receptor-Mediated ATP Currents in Rat Dorsal Root Ganglion Neurons

Purinergic signaling is involved in multiple pain processes. P2X3 receptor is a key target in pain therapeutics, while A1 adenosine receptor signaling plays a role in analgesia. However, it remains unclear whether there is a link between them in pain. The present results showed that the A1 adenosine receptor agonist N⁶-cyclopentyladenosine (CPA) concentration dependently suppressed P2X3 receptor-mediated and α,β-methylene-ATP (α,β-meATP)-evoked inward currents in rat dorsal root ganglion (DRG) neurons. CPA significantly decreased the maximal current response to α,β-meATP, as shown a downward shift of the concentration-response curve for α,β-meATP. CPA suppressed ATP currents in a voltage-independent manner. Inhibition of ATP currents by CPA was completely prevented by the A1 adenosine receptor antagonist KW-3902, and disappeared after the intracellular dialysis of either the G_i/o protein inhibitor pertussis toxin, the adenylate cyclase activator forskolin, or the cAMP analog 8-Br-cAMP. Moreover, CPA suppressed the membrane potential depolarization and action potential bursts, which were induced by α,β-meATP in DRG neurons. Finally, CPA relieved α,β-meATP-induced nociceptive behaviors in rats by activating peripheral A1 adenosine receptors. These results indicated that CPA inhibited the activity of P2X3 receptors in rat primary sensory neurons by activating A1 adenosine receptors and its downstream cAMP signaling pathway, revealing a novel peripheral mechanism underlying its analgesic effect.

Caffeine Attenuates Electroacupuncture Effect on Pressure Pain Threshold and Tolerance in Healthy Individuals: A Randomized Controlled Trial

Introduction

The effect of caffeine on acupuncture analgesia in humans is unclear. This study aimed to investigate whether caffeine-containing beverage intake influences the effect of electroacupuncture (EA) on static quantitative sensory testing (QST) and dynamic QST in healthy subjects.

Methods

A total of 40 healthy subjects were enrolled and randomly assigned to receive coffee containing moderate doses of caffeine (coffee group) or non-caffeinated juice (juice group) for 4 weeks. The primary outcome measures were the pressure pain threshold (PPT), pressure pain tolerance (PPTo), and heat pain threshold (HPT) as static QST parameters. Numerical rating scales (NRS) of heat stimulus and nociceptive flexor reflex (RIII reflex), as parameters of dynamic QST, were also examined. EA stimulation with tolerance intensity was performed at ST36 (Zusanli)-GB34 (Yanglingquan) points at weeks 0, 2, and 4. PPT, PPTo, and HPT were detected pre- and post- EA. The NRS scores were examined pre-, during, and post-EA, and 1 min after EA was completed. The RIII reflex was examined pre- and 1–5 min post-EA.

Results

At week 0, both groups showed increased PPT and PPTo and decreased NRS scores of heat stimuli and RIII reflex after EA, but HPT was not affected. After 4 weeks, the effects of EA on PPT and PPTo were attenuated in the coffee group compared to the juice group, whereas the effect of EA on the NRS scores and RIII reflex were not influenced. There was no significant difference found at week 2 for these indications. EA also did not affect the HPT in both groups at week 4.

Conclusion

Moderate caffeine intake reduced the effects of EA on PPT and PPTo in healthy subjects.

Caffeine: What Is Its Role in Pain Medicine?

Caffeine is the world's most widely used psychoactive legal substance. The involvement of caffeine in pain management has gotten minimal attention in the past, but it is getting more attention now. This article provides a brief assessment of the literature to clarify the role of caffeine as a pain reliever and stimulate the interest of researchers. Caffeine affects adenosine receptors, which are involved in nociception, and plays a significant role in pain regulation. Caffeine's usage as an adjuvant therapy has been extensively documented in the literature, and it is now accessible in certain over-the-counter drugs. The mixture of coffee and morphine for pain reduction in individuals with terminal cancer has shown mixed outcomes in studies. Caffeine can be utilized for hypnic headaches and post-dural puncture headaches since it is crucial in pain regulation. Caffeine has the potential to help in pain management. Caffeine's usage for migraines and end-stage cancer disease is not well acknowledged. Further research is essential to focus on caffeine's potential role in various forms of pain, including dosage escalation and outcome assessment standardization.

Effective Oriental Magic for Analgesia: Acupuncture

Pain is a kind of complex physiological and psychological symptom, which makes the person debilitated and uncomfortable. Some persistent pain is unbearable for the patients, reducing the quality of life and bringing considerable pressure to the individuals and society. Pain killers seem to be effective in analgesia for patients, but their safety and addiction are crucial issues. From the theory of traditional Chinese medicine (TCM), the blocked meridian is the main cause of pain, and effective acupuncture can play a positive analgesic effect. Acupuncture that can date back thousands of years is one of the ancient medical practices in China. Its safety and effectiveness are respected. Based on its superior safety and inferior side effects, it has been gradually recognized as a therapeutic intervention method for complementary medicine, which is also generally used to treat multiple pain diseases. It is shown by modern medical studies that neurotransmitters are the material basis for the acupuncture effect, and the effect of acupuncture analgesia is related to changes in neurotransmitters. However, the specific mechanism has not been elucidated. This review aims to comprehensively discuss the historical evolution of acupuncture analgesia, clinical research of acupuncture analgesia, comparison of acupuncture and drug therapy, the neurotransmitter mechanism of acupuncture analgesia, the effect of acupuncture manipulation on analgesia, and bibliometric analysis of acupuncture treatment for pain, to explore the superiority and related mechanism of acupuncture analgesia from different aspects, and to provide a more effective treatment for alleviating patients' pain.

Adenosine receptors: Emerging non-opioids targets for pain medications

Physical and emotional pain deteriorates the quality of well-being. Also, numerous non-invasive and invasive treatments for diagnosed diseases such as cancer medications and surgical procedures cause various types of pain. Despite the multidisciplinary approaches available to manage pain, the unmet needs for medication with minimal side effects are substantial. Especially with the surge of opioid crisis during the last decades, non-opioid analgesics may reduce life-threatening overdosing and addictive liability. Although many clinical trials supported the potential potency of cannabis and cannabidiol (CBD) in pain management or treatment, the long-term benefits of cannabis or CBD are still not evident. At the same time, growing evidence shows the risk of overusing cannabis and CBD. Therefore, it is urgent to develop novel analgesic medications that minimize side effects. All four well-identified adenosine receptors, A₁, A_2A, A_2B, and A₃, are implicated in pain. Recently, a report demonstrated that an adenosine A₁R-specific positive allosteric modulator (PAM) is a potent analgesic without noticeable side effects. Also, several A₃R agonists are being considered as promising analgesic agent. However, the importance of adenosine in pain is relatively underestimated. To help readers understand, first, we will summarize the historical perspective of the adenosine system in preclinical and clinical studies. Then, we will discuss possible interactions of adenosine and opioids or the cannabis system focusing on pain. Overall, this review will provide the potential role of adenosine and adenosine receptors in pain treatment.

Role of Purinergic Signaling in Acupuncture Therapeutics

Acupuncture is a therapeutic treatment that is well recognized in many countries. However, the initiation mechanisms of acupuncture are not well understood. Purinergic signaling has been considered a key signaling pathway in acupuncture in recent years. Acupuncture-induced ATP is mainly produced by mast cells and fibroblasts, and ATP is gradually hydrolyzed into adenosine. ATP and adenosine further participate in the process of acupuncture information transmission to the nervous and immune systems through specific purine receptors. Acupuncture initiates analgesia via the down-regulation of the expression of P2 receptors or up-regulation of the expression of adenosine A₁ receptors on nerve fibers. ATP also promotes the proliferation of immune cells through P2 receptors and A₃ receptors, causing inflammation. In contrast, adenosine activates A₂ receptors, promotes the production and infiltration of immunosuppressive cells, and causes an anti-inflammatory response. In summary, we described the role of purinergic signaling as a general signaling pathway in the initiation of acupuncture and the influence of purinergic signaling on the neuroimmune network to lay the foundation for future systematic research on the mechanisms of acupuncture therapeutics.

Peripheral receptors and neuromediators involved in the antihyperalgesic effects of acupuncture: a state-of-the-art review

The present study aims to describe state-of-the-art of preclinical studies that have investigated peripheral receptors and neuromediators involved in the antihyperalgesic effects of acupuncture. The PubMed, Scopus, and Web of Science databases were searched using the integrative review method. Preclinical articles that involved the study of peripheral receptors and neuromediators on the pain control effects of acupuncture in rats or mice were selected using a predefined search strategy. From this search, 456 articles were found, and 29 of them met the inclusion criteria of the study. The selected articles addressed the following peripheral receptors: opioid (n = 9), adenosine (n = 5), cannabinoid (n = 5), transient receptor potential vanilloid (TRPV) (n = 3), histamine (n = 2), adrenergic (n = 1), muscarinic (n = 1), corticotrophin-releasing factor (CRF) (n = 2), IL-1 (n = 1), and endothelin (n = 1) receptors. The peripheral neuromediators correlated with the peripheral pain control effect were as follows: opioid peptides (n = 4), adenosine (n = 3), histamine (n = 1), substance P (n = 1) calcitonin gene-related peptide (CGRP) (n = 1), anandamide (n = 1), nitric oxide (n = 1), and norepinephrine (n = 1). This review summarizes the methods used to investigate the peripheral effects of acupuncture and discusses the main findings on each family of receptors and neuromediators. Ten families of peripheral receptors and 8 types of neuromediators were correlated with the antihyperalgesic effects of acupuncture in preclinical studies. Considering the benefits of a better understanding of the role of peripheral receptors and neuromediators in the context pain management, the findings of the present study highlight the importance of deepening the exploration of the peripheral mechanisms of acupuncture.

Augmented Mechanical Forces of the Surface-Modified Nanoporous Acupuncture Needles Elicit Enhanced Analgesic Effects

Over the past several decades, clinical studies have shown significant analgesic effects of acupuncture. The efficacy of acupuncture treatment has improved with the recent development of nanoporous needles (PN), which are produced by modifying the needle surface using nanotechnology. Herein, we showed that PN at acupoint ST36 produces prolonged analgesic effects in an inflammatory pain model; the analgesic effects of PN acupuncture were sustained over 2 h, while those using a conventional needle (CN) lasted only 30 min. In addition, the PN showed greater therapeutic effects than CN after 10 acupuncture treatments once per day for 10 days. We explored how the porous surface of the PN contributes to changes in local tissue, which may in turn result in enhanced analgesic effects. We showed that the PN has greater rotational torque and pulling force than the CN, particularly at acupoints ST36 and LI11, situated on thick muscle layers. Additionally, in ex vivo experiments, the PN showed greater winding of subcutaneous connective tissues and muscle layers. Our results suggest that local mechanical forces are augmented by the PN and its nanoporous surface, contributing to the enhanced and prolonged analgesic effects of PN acupuncture.

Acupuncture and Neural Mechanism in the Management of Low Back Pain-An Update

Within the last 10 years, the percentage of low back pain (LBP) prevalence increased by 18%. The management and high cost of LBP put a tremendous burden on the healthcare system. Many risk factors have been identified, such as lifestyle, trauma, degeneration, postural impairment, and occupational related factors; however, as high as 95% of the cases of LBP are non-specific. Currently, LBP is treated pharmacologically. Approximately 25 to 30% of the patients develop serious side effects, such as drowsiness and drug addiction. Spinal surgery often does not result in a massive improvement of pain relief. Therefore, complementary approaches are being integrated into the rehabilitation programs. These include chiropractic therapy, physiotherapy, massage, exercise, herbal medicine and acupuncture. Acupuncture for LBP is one of the most commonly used non-pharmacological pain-relieving techniques. This is due to its low adverse effects and cost-effectiveness. Currently, many randomized controlled trials and clinical research studies have produced promising results. In this article, the causes and incidence of LBP on global health care are reviewed. The importance of treatment by acupuncture is considered. The efforts to reveal the link between acupuncture points and anatomical features and the neurological mechanisms that lead to acupuncture-induced analgesic effect are reviewed.

Electroacupuncture Attenuates Induction of Inflammatory Pain by Regulating Opioid and Adenosine Pathways in Mice

Although inflammatory pain is a common clinical condition, its mechanisms are still unclear. Electroacupuncture (EA), a well-known method of pain management, may reduce inflammatory pain by regulating neurons, astrocytes, and inflammatory signaling pathways. Injections of complete Freund’s adjuvant (CFA), which can initiate cell-mediated inflammatory pain, resulted in significant hyperalgesia, which was subsequently prevented by EA. In CFA-injected mice, a dramatic increase was observed in the expression of the following proteins in the dorsal root ganglion and spinal cord dorsal horn: the astrocytic marker GFAP, S100B, RAGE, pPKCε, COX-2, pERK, and pNFκB. These effects were reversed by EA. In addition, mechanical hyperalgesia was significantly reduced in the N6-cyclopentyladenosine (CPA) i.p. or i.m. and endomorphin (EM) i.p. groups. Neither EM i.m. nor EM i.p. exhibited any analgesic effect on thermal hyperalgesia. However, both CPA i.m. and CPA i.p. attenuated thermal hyperalgesia in the mouse inflammatory pain model. We showed that CPA reduced COX-2 and pPKCε expression. However, EM administration did not reduce COX-2 levels. Combined administration of naloxone and rolofylline increased pPKCε and COX-2 pathways. Taken together, our study results revealed a novel and detailed mechanism of EA-induced analgesia that involves the regulation of the opioid and adenosine pathways.

Effects of Electroacupuncture on Methamphetamine-Induced Behavioral Changes in Mice

Methamphetamine (METH) is a major drug of abuse worldwide, and no efficient therapeutic strategies for treating METH addiction are currently available. Continuous METH use can cause behavioral upregulation or psychosis. The dopaminergic pathways, particularly the neural circuitry from the ventral tegmental area to the nucleus accumbens (NAc), have a critical role in this behavioral stage. Acupuncture has been used for treating diseases in China for more than 2000 years. According to a World Health Organization report, acupuncture can be used to treat several functional disorders, including substance abuse. In addition, acupuncture is effective against opioids addiction. In this study, we used electroacupuncture (EA) for treating METH-induced behavioral changes and investigated the possible therapeutic mechanism. Results showed that EA at the unilateral Zhubin (KI9)–Taichong (LR3) significantly reduced METH-induced behavioral sensitization and conditioned place preference. In addition, both dopamine and tyrosine hydroxylase (TH) levels decreased but monoamine oxidase A (MAO-A) levels increased in the NAc of the METH-treated mice receiving EA compared with those not receiving EA. EA may be a useful nonpharmacological approach for treating METH-induced behavioral changes, probably because it reduces the METH-induced TH expression and dopamine levels and raises MAO-A expression in the NAc.

The Role of Caffeine in Pain Management: A Brief Literature Review

CONTEXT

Caffeine is the most commonly used psychoactive legal drug in the world. Caffeine's role in controlling pain has received less attention in the past, yet is being increasingly considered. This article briefly reviewed the literature to clarify the role of caffeine as a drug for pain control and attract investigators to this topic.

EVIDENCE ACQUISITION

The data on Caffeine as an adjuvant therapy or as a main component for pain modulation has been narratively reviewed.

RESULTS

Caffeine plays an important role in pain modulation through their action on adenosine receptors which are involved in nociception. The use of caffeine as adjuvant treatment was well-established in the literature and caffeine is currently available in some over the counter medications. Studies showed controversial results about the interaction between caffeine and morphine for pain relief in patients with terminal stage cancer. As a main component for pain modulation, Caffeine can be used for hypnic headache and postdural puncture headache.

CONCLUSIONS

Caffeine has a potential role for pain modulation. Current evidence on caffeine use for migraine and terminal stage cancer is not well-established. Future studies should address the use of caffeine alone for different types of pain with dose escalation and standardization of outcome measurement.

Repeated Electroacupuncture Persistently Elevates Adenosine and Ameliorates Collagen-Induced Arthritis in Rats

The aim of this paper was to investigate the effect of repeated electroacupuncture (EA) over 21 days on the adenosine concentration in peripheral blood of rats with collagen-induced arthritis (CIA). Wistar rats were divided into three groups of 6 animals each: sham-control, CIA-control, and CIA-EA. We determined the adenosine concentration in peripheral blood and assessed pathological changes of ankle joints. Quantitative reverse-transcription-polymerase chain reaction was used to determine mRNA levels of ecto-5'-nucleotidase (CD73), adenosine deaminase (ADA), and tumor necrosis factor-alpha (TNF-α). Immunohistochemical staining was used to detect expression of ADA and CD73 in synovial tissue. Repeated EA treatment on CIA resulted in the persistence of high concentrations of adenosine in peripheral blood, significantly reduced pathological scores, TNF-α mRNA concentrations, and synovial hyperplasia. Importantly, EA treatment led to a significant increase in CD73 mRNA levels in peripheral blood but was associated with a decrease of CD73 immunostaining in synovial tissue. In addition, EA treatment resulted in a significant decrease of both ADA mRNA levels in peripheral blood and ADA immunostaining in synovial tissue. Thus, repeated EA treatment exerts an anti-inflammatory and immunoregulatory effect on CIA by increasing the concentration of adenosine. The mechanism of EA action may involve the modulation of CD73 and ADA expression levels.

Mast cell-nerve cell interaction at acupoint: modeling mechanotransduction pathway induced by acupuncture

Mast cells are found abundant at sites of acupoints. Nerve cells share perivascular localization with mast cells. Acupuncture (mechanical stimuli) can activate mast cells to release adenosine triphosphate (ATP) which can activate nerve cells and modulates pain-processing pathways in response to acupuncture. In this paper, a mathematical model was constructed for describing intracellular Ca²⁺ signal and ATP release in a coupled mast cell and nerve cell system induced by mechanical stimuli. The results showed mechanical stimuli lead to a intracellular Ca²⁺ rise in the mast cell and ATP release, ATP diffuses in the extracellular space (ECS) and activates the nearby nerve cells, then induces electrical current in the nerve cell which spreads in the neural network. This study may facilitate our understanding of the mechanotransduction process induced by acupuncture and provide a methodology for quantitatively analyzing acupuncture treatment.

Caffeine at Moderate Doses Can Inhibit Acupuncture-Induced Analgesia in a Mouse Model of Postoperative Pain

BACKGROUND

The use of acupuncture in the treatment of pain conditions has been extensively investigated. However, the influence of dietary ingredients on acupuncture-induced analgesia (AA) remains unexplored. Recently, the role of adenosine receptors in AA has been shown, and caffeine, one of the world's most commonly consumed dietary ingredients, is an antagonist of these receptors. In this study, the postincisional pain model was used to investigate caffeine's influence on AA.

METHOD

Mice submitted to plantar incision surgery were treated with acupuncture needling after administration of acute or chronic caffeine. Acupuncture needling was performed using two different types of stimuli, manual acupuncture and electroacupuncture bilaterally in the acupoint SP6.

RESULTS

We found that acute preadministration of caffeine (10 mg/kg, i.p.) completely reversed AA in both types of acupuncture. In the chronic preadministration, we used two doses that mimicked the average daily caffeine consumption in Western countries and China. Interestingly, the Western dose of caffeine (70 mg/kg/day) administered during 8 days in the drinking water reversed AA and the Chinese dose (4 mg/kg/day) administered during the same period did not.

CONCLUSIONS

These results indicate that the use of caffeine can inhibit the analgesic effect of different forms of acupuncture. In addition, our findings suggest that doses of caffeine relevant to dietary human intake levels could be a confounding factor in the context of acupuncture research.

Ankle joint mobilization affects postoperative pain through peripheral and central adenosine A1 receptors

BACKGROUND

Physical therapists frequently use joint mobilization therapy techniques to treat people with musculoskeletal dysfunction and pain. Several studies suggest that endogenous adenosine may act in an analgesic fashion in various pain states.

OBJECTIVE

The purpose of this study was to investigate the contribution of the adenosinergic system on the antihyperalgesic effect of ankle joint mobilization (AJM).

DESIGN

This was a experimental study.

METHODS

To test the hypothesis that the adrenosinergic system is involved in the antihyperalgesic effect of AJM, mice (25-35 g) submitted to plantar incision surgery were used as a model of acute postoperative pain. The mice were subjected to AJM for 9 minutes. Withdrawal frequency to mechanical stimuli was assessed 24 hours after plantar incision surgery and 30 minutes after AJM, adenosine, clonidine, or morphine treatments. The adenosinergic system was assessed by systemic (intraperitoneal), central (intrathecal), and peripheral (intraplantar) administration of caffeine. The participation of the A1 receptor was investigated using a selective adenosine A1 receptor subtype antagonist. In addition, previous data on the involvement of the serotonergic and noradrenergic systems in the antihyperalgesic effect of AJM were confirmed.

RESULTS

Ankle joint mobilization decreased mechanical hyperalgesia, and this effect was reversed by pretreatment of the animals with caffeine given by intraperitoneal, intraplantar, and intrathecal routes. In addition, intraplanar and intrathecal administrations of 1,3-dipropyl-8-cyclopentylxanthine (DPCPX, a selective adenosine A1 subtype receptor antagonist) or systemic administration of yohimbine or ρ-chlorophenylalanine methyl ester hydrochloride (PCPA) blocked the antihyperalgesia induced by AJM.

LIMITATIONS

The results are limited to animal models and cannot be generalized to acute pain in humans.

CONCLUSIONS

This study demonstrated the involvement of the adenosinergic system in the antihyperalgesic effect of AJM in a rodent model of pain and provides a possible mechanism basis for AJM-induced relief of acute pain.

Purine receptor mediated actin cytoskeleton remodeling of human fibroblasts

Earlier studies have shown that activation of adenosine A1 receptors on peripheral pain fibers contributes to acupuncture-induced suppression of painful input. In addition to adenosine, acupuncture triggers the release of other purines, including ATP and ADP that may bind to purine receptors on nearby fibroblasts. We here show that purine agonists trigger increase in cytosolic Ca(2+) signaling in a cultured human fibroblasts cell line. The profile of agonist-induced Ca(2+) increases indicates that the cells express functional P2yR2 and P2yR4 receptors, as well as P2yR1 and P2xR7 receptors. Unexpectedly, purine-induced Ca(2+) signaling was associated with a remodeling of the actin cytoskeleton. ATP induced a transient loss in F-actin stress fiber. The changes of actin cytoskeleton occurred slowly and peaked at 10min after agonist exposure. Inhibition of ATP-induced increases in Ca(2+) by cyclopiazonic acid blocked receptor-mediated cytoskeleton remodeling. The Ca(2+) ionophore failed to induce cytoskeletal remodeling despite triggering robust increases in cytosolic Ca(2+). These observations indicate that purine signaling induces transient changes in fibroblast cytoarchitecture that could be related to the beneficial effects of acupuncture.

Does acupuncture activate endogenous analgesia in chronic whiplash-associated disorders? A randomized crossover trial

BACKGROUND

Many patients with chronic pain, including those with chronic whiplash-associated disorders (WAD), show features of central sensitization. Randomized trials examining whether treatments are able to influence the process of central sensitization in patients with chronic WAD are emerging. Therefore, the present study aimed at examining whether acupuncture results in activation of endogenous analgesia and relief in symptoms in patients with chronic WAD.

METHODS

In this randomized crossover pilot trial with blinded assessors, each patient (n = 39) received two treatment sessions of identical duration, with acupuncture and relaxation therapy randomly crossed over in visit 2. Primary outcome measurement included immediate activation of endogenous analgesia i.e., pressure pain sensitivity and conditioned pain modulation. Secondary outcome measurements included pain relief and reduced disability level.

RESULTS

Local pressure pain sensitivity at baseline and during conditioned pain modulation decreased significantly more following acupuncture compared with relaxation (time × group interactions: p < 0.001), both in the neck and at a site distinct from the painful region. When comparing the effects of acupuncture versus relaxation, no differences were observed on conditioned pain modulation, temporal summation of pressure pain, neck disability or symptom severity (all p-values >0.05).

CONCLUSION

It was shown that one session of acupuncture treatment results in acute improvements in pressure pain sensitivity in the neck and calf of patients with chronic WAD. Acupuncture had no effect on conditioned pain modulation or temporal summation of pressure pain. Both acupuncture and relaxation appear to be well-tolerated treatments for people with chronic WAD. These findings suggest that acupuncture treatment activates endogenous analgesia in patients with chronic WAD.

Pain-relieving prospects for adenosine receptors and ectonucleotidases

Adenosine receptor agonists have potent antinociceptive effects in diverse preclinical models of chronic pain. By contrast, the efficacy of adenosine and adenosine receptor agonists in treating pain in humans is unclear. Two ectonucleotidases that generate adenosine in nociceptive neurons were recently identified. When injected spinally, these enzymes have long-lasting adenosine A(1) receptor-dependent antinociceptive effects in inflammatory and neuropathic pain models. Furthermore, recent findings indicate that spinal adenosine A(2A) receptor activation can enduringly inhibit neuropathic pain symptoms. Collectively, these studies suggest the possibility of treating chronic pain in humans by targeting specific adenosine receptor subtypes in anatomically defined regions with agonists or with ectonucleotidases that generate adenosine.