A role for substance P and acid-sensing ion channel 1a in prolotherapy with dextrose-mediated analgesia in a mouse model of chronic muscle pain

Genetic exploration of roles of acid-sensing ion channel subtypes in neurosensory mechanotransduction including proprioception

Although acid-sensing ion channels (ASICs) are proton-gated ion channels responsible for sensing tissue acidosis, accumulating evidence has shown that ASICs are also involved in neurosensory mechanotransduction. However, in contrast to Piezo ion channels, evidence of ASICs as mechanically gated ion channels has not been found using conventional mechanoclamp approaches. Instead, ASICs are involved in the tether model of mechanotransduction, with the channels gated via tethering elements of extracellular matrix and intracellular cytoskeletons. Methods using substrate deformation-driven neurite stretch and micropipette-guided ultrasound were developed to reveal the roles of ASIC3 and ASIC1a, respectively. Here we summarize the evidence supporting the roles of ASICs in neurosensory mechanotransduction in knockout mouse models of ASIC subtypes and provide insight to further probe their roles in proprioception.

Role of proprioceptors in chronic musculoskeletal pain

Proprioceptors are non-nociceptive low-threshold mechanoreceptors. However, recent studies have shown that proprioceptors are acid-sensitive and express a variety of proton-sensing ion channels and receptors. Accordingly, although proprioceptors are commonly known as mechanosensing neurons that monitor muscle contraction status and body position, they may have a role in the development of pain associated with tissue acidosis. In clinical practice, proprioception training is beneficial for pain relief. Here we summarize the current evidence to sketch a different role of proprioceptors in 'non-nociceptive pain' with a focus on their acid-sensing properties.

Distribution and Chemistry of Phoenixin-14, a Newly Discovered Sensory Transmission Molecule in Porcine Afferent Neurons

Phoenixin-14 (PNX), initially discovered in the rat hypothalamus, was also detected in dorsal root ganglion (DRG) cells, where its involvement in the regulation of pain and/or itch sensation was suggested. However, there is a lack of data not only on its distribution in DRGs along individual segments of the spinal cord, but also on the pattern(s) of its co-occurrence with other sensory neurotransmitters. To fill the above-mentioned gap and expand our knowledge about the occurrence of PNX in mammalian species other than rodents, this study examined (i) the pattern(s) of PNX occurrence in DRG neurons of subsequent neuromeres along the porcine spinal cord, (ii) their intraganglionic distribution and (iii) the pattern(s) of PNX co-occurrence with other biologically active agents. PNX was found in approximately 20% of all nerve cells of each DRG examined; the largest subpopulation of PNX-positive (PNX+) cells were small-diameter neurons, accounting for 74% of all PNX-positive neurons found. PNX+ neurons also co-contained calcitonin gene-related peptide (CGRP; 96.1%), substance P (SP; 88.5%), nitric oxide synthase (nNOS; 52.1%), galanin (GAL; 20.7%), calretinin (CRT; 10%), pituitary adenylate cyclase-activating polypeptide (PACAP; 7.4%), cocaine and amphetamine related transcript (CART; 5.1%) or somatostatin (SOM; 4.7%). Although the exact function of PNX in DRGs is not yet known, the high degree of co-localization of this peptide with the main nociceptive transmitters SP and CGRP may suggests its function in modulation of pain transmission.

Effectiveness of Hypertonic Dextrose Injection (Prolotherapy) in Plantar Fasciopathy: A Systematic Review and Meta-analysis of Randomized Controlled Trials

OBJECTIVE

To systematically review the effectiveness of hypertonic dextrose prolotherapy (DPT) in plantar fasciopathy (PF) compared with other non-surgical treatments.

DATA SOURCES

PubMed/MEDLINE, EMBASE, Cochrane Central Register of Controlled Trials, Web of Science, Allied and Complementary Medicine Database, Global Health, Ovid Nursing Database, Dimensions, and WHO ICTRP were searched from inception to April 30th, 2022.

STUDY SELECTION

Two independent reviewers selected randomized controlled trials (RCTs) that evaluated the effectiveness of DPT in PF compared with non-surgical treatments. Outcomes included pain intensity, foot and ankle function, and plantar fascia thickness.

DATA EXTRACTION

Two independent reviewers conducted data extraction. Risk of bias (RoB) assessment was conducted using the Cochrane Risk of Bias 2 (RoB 2) tool, and certainty of evidence was assessed with Grading of Recommendation Assessment, Development, and Evaluation (GRADE).

DATA SYNTHESIS

Eight RCTs (n=469) met the inclusion criteria. Pooled results favored the use of DPT versus normal saline (NS) injections in reducing pain (weighted mean difference [WMD] -41.72; 95% confidence interval [CI] -62.36 to -21.08; P<.01; low certainty evidence) and improving function [WMD -39.04; 95% CI -55.24 to -22.85; P<.01; low certainty evidence] in the medium term. Pooled results also showed corticosteroid (CS) injections was superior to DPT in reducing pain in the short term [standardized mean difference 0.77; 95% CI 0.40 to 1.14; P<.01; moderate certainty evidence]. Overall RoB varied from "some concerns" to "high". The overall certainty of evidence presented ranges from very low to moderate based on the assessment with the GRADE approach.

CONCLUSION

Low certainty evidence demonstrated that DPT was superior to NS injections in reducing pain and improving function in the medium term, but moderate certainty evidence showed that it was inferior to CS in reducing pain in the short term. Further high-quality RCTs with standard protocol, longer-term follow-up, and adequate sample size are needed to confirm its role in clinical practice.

A comparison between hypertonic dextrose prolotherapy and conventional physiotherapy in patients with knee osteoarthritis

The aim of the present study was to compare the efficacy of hypertonic dextrose prolotherapy (HDP) with conventional physiotherapy (CPT) in improving symptoms in females with knee osteoarthritis (OA). The present study included 60 patients with a diagnosis of knee OA. The patients were randomly assigned to the HDP (n=30) and CPT (n=30) groups. The patients in the HDP group were treated with a dextrose injection into the knee joint (25% dextrose) and around the knee (15% dextrose) in two sessions for 1 month, while those in the CPT group received a hot pack, transcutaneous electrical nerve stimulation and therapeutic ultrasound in five sessions a week for 4 weeks. Prior to commencing the treatment, and at 1 and 3 months post-treatment, all the patients were evaluated using the visual analog scale (VAS), Western Ontario and McMaster Osteoarthritis Index (WOMAC), the goniometric measurement of active knee range of motion (ROM), a 50-m walking test and isokinetic knee muscle strength measurements. There were no statistically significant differences between the two groups as regards the demographic characteristics at pre-treatment (P>0.05). However, at 1 and 3 months post-treatment, the scores of all the outcome parameters were significantly improved in the HDP group compared with the CPT group (P<0.05 for all). In both groups, a significant improvement was observed in the VAS scores, WOMAC total values and ROM following the treatments, with the greatest improvement observed in the HDP group (P<0.001). The isokinetic quadriceps peak torque measurements were increased in both groups following treatment. All the scores exhibited a statistically significant improvement in the HDP group at both 1 and 3 months post-treatment. On the whole, the results of the present study demonstrate that both HDP and CPT are effective treatment modalities to relieve pain, and increase functionality and strength in patients with knee OA. However, greater improvements in pain and functionality can be achieved with prolotherapy.

Involvement of ASIC3 and Substance P in Therapeutic Ultrasound-Mediated Analgesia in Mouse Models of Fibromyalgia

Therapeutic ultrasound (tUS) is widely used in chronic muscle pain control. However, its analgesic molecular mechanism is still not known. Our objective is to reveal the mechanism of the tUS-induced analgesia in mouse models of fibromyalgia. We applied tUS in mice that have developed chronic hyperalgesia induced by intramuscular acidification and determined the tUS frequency at 3 MHz, dosage at 1 W/cm2 (measured output as 6.3 mW/cm2) and 100% duty cycle for 3 minutes having the best analgesic effect. Pharmacological and genetic approaches were used to probe the molecular determinants involved in tUS-mediated analgesia. A second mouse model of fibromyalgia induced by intermittent cold stress was further used to validate the mechanism underlying the tUS-mediated analgesia. The tUS-mediated analgesia was abolished by a pretreatment of NK1 receptor antagonist-RP-67580 or knockout of substance P (Tac1-/-). Besides, the tUS-mediated analgesia was abolished by ASIC3-selective antagonist APETx2 but not TRPV1-selective antagonist capsazepine, suggesting a role for ASIC3. Moreover, the tUS-mediated analgesia was attenuated by ASIC3-selective nonsteroid anti-inflammation drugs (NSAIDs)-aspirin and diclofenac but not by ASIC1a-selective ibuprofen. We next validated the antinociceptive role of substance P signaling in the model induced by intermittent cold stress, in which tUS-mediated analgesia was abolished in mice lacking substance P, NK1R, Asic1a, Asic2b, or Asic3 gene. tUS treatment could activate ASIC3-containing channels in muscle afferents to release substance P intramuscularly and exert an analgesic effect in mouse models of fibromyalgia. NSAIDs should be cautiously used or avoided in the tUS treatment. PERSPECTIVE: Therapeutic ultrasound showed analgesic effects against chronic mechanical hyperalgesia in the mouse model of fibromyalgia through the signaling pathways involving substance P and ASIC3-containing ion channels in muscle afferents. NSAIDs should be cautiously used during tUS treatment.

Acidosis-related pain and its receptors as targets for chronic pain

Sensing acidosis is an important somatosensory function in responses to ischemia, inflammation, and metabolic alteration. Accumulating evidence has shown that acidosis is an effective factor for pain induction and that many intractable chronic pain diseases are associated with acidosis signaling. Various receptors have been known to detect extracellular acidosis and all express in the somatosensory neurons, such as acid sensing ion channels (ASIC), transient receptor potential (TRP) channels and proton-sensing G-protein coupled receptors. In addition to sense noxious acidic stimulation, these proton-sensing receptors also play a vital role in pain processing. For example, ASICs and TRPs are involved in not only nociceptive activation but also anti-nociceptive effects as well as some other non-nociceptive pathways. Herein, we review recent progress in probing the roles of proton-sensing receptors in preclinical pain research and their clinical relevance. We also propose a new concept of sngception to address the specific somatosensory function of acid sensation. This review aims to connect these acid-sensing receptors with basic pain research and clinical pain diseases, thus helping with better understanding the acid-related pain pathogenesis and their potential therapeutic roles via the mechanism of acid-mediated antinociception.

A protocol for a randomized clinical trial assessing the efficacy of hypertonic dextrose injection (prolotherapy) in chronic ankle instability

BACKGROUND

Lateral ankle sprain (LAS) is a common injury. Conservative care is not uniformly effective. Chronic ankle instability (CAI) results in up to 70% of patients with LAS in the physically active population. LAS, together with subsequent osteochondral lesions and pain in many patients, leads to the development of post-traumatic osteoarthritis, resulting in a substantial direct and indirect personal and societal health burden. Dextrose prolotherapy (DPT) is an injection-based therapy for many chronic musculoskeletal conditions but has not been tested for CAI. This protocol describes a randomized controlled trial to test the efficacy of DPT versus normal saline (NS) injections for chronic ankle instability (CAI).

METHODS AND ANALYSIS

A single-center, parallel-group, randomized controlled trial will be conducted at a university-based primary care clinic in Hong Kong. A total of 114 patients with CAI will be randomly allocated (1:1) to DPT and NS groups. The primary outcome will be the Cumberland Ankle Instability Tool scores at 1 year. The secondary outcomes will be the number of re-sprains in 1 year, the Star Excursion Balance Test, the 5-level of EuroQol 5-dimension questionnaire, and the Foot and Ankle Ability Measure. All outcomes will be evaluated at baseline and at 16, 26, and 52 weeks using a linear mixed model.

DISCUSSION

We hypothesized the DPT is a safe, easily accessible, and effective treatment for patients with CAI. This RCT study will inform whether DPT could be a primary non-surgical treatment for CAI.

TRIAL REGISTRATION

Chinese Clinical Trial Registry ChiCTR2000040213 . Registered on 25 November 2020.

Cell-based therapeutic strategies for treatment of spinocerebellar ataxias: an update

Spinocerebellar ataxias are heritable neurodegenerative diseases caused by a cytosine-adenine-guanine expansion, which encodes a long glutamine tract (polyglutamine) in the respective wild-type protein causing misfolding and protein aggregation. Clinical features of polyglutamine spinocerebellar ataxias include neuronal aggregation, mitochondrial dysfunction, decreased proteasomal activity, and autophagy impairment. Mutant polyglutamine protein aggregates accumulate within neurons and cause neural dysfunction and death in specific regions of the central nervous system. Spinocerebellar ataxias are mostly characterized by progressive ataxia, speech and swallowing problems, loss of coordination and gait deficits. Over the past decade, efforts have been made to ameliorate disease symptoms in patients, yet no cure is available. Previous studies have been proposing the use of stem cells as promising tools for central nervous system tissue regeneration. So far, pre-clinical trials have shown improvement in various models of neurodegenerative diseases following stem cell transplantation, including animal models of spinocerebellar ataxia types 1, 2, and 3. However, contrasting results can be found in the literature, depending on the animal model, cell type, and route of administration used. Nonetheless, clinical trials using cellular implants into degenerated brain regions have already been applied, with the expectation that these cells would be able to differentiate into the specific neuronal subtypes and re-populate these regions, reconstructing the affected neural network. Meanwhile, the question of how feasible it is to continue such treatments remains unanswered, with long-lasting effects being still unknown. To establish the value of these advanced therapeutic tools, it is important to predict the actions of the transplanted cells as well as to understand which cell type can induce the best outcomes for each disease. Further studies are needed to determine the best route of administration, without neglecting the possible risks of repetitive transplantation that these approaches so far appear to demand. Despite the challenges ahead of us, cell-transplantation therapies are reported to have transient but beneficial outcomes in spinocerebellar ataxias, which encourages efforts towards their improvement in the future.

Activation of Mechanosensitive Ion Channels by Ultrasound

Mechanosensitive channels (MSCs) play an important role in how cells transduce mechanical stimuli into electrical or chemical signals, which provides an interventional possibility through the manipulation of ion channel activation using different mechanical stimulation conditions. With good spatial resolution and depth of penetration, ultrasound is often proposed as the tool of choice for such therapeutic applications. Despite the identification of many ion channels as mechanosensitive in recent years, only a limited number of MSCs have been reported to be activated by ultrasound with substantial evidence. Furthermore, although many therapeutic implications using ultrasound have been explored, few offered insights into the molecular basis and the biological effects induced by ultrasound in relieving pain and accelerate tissue healing. In this review, we examined the literature, in particular studies that provided evidence of cellular responses to ultrasound, with and without the target ion channels. The ultrasound activation conditions were then summarized for these ion channels, and these conditions were related to their mode of activation based on the current biological concepts. The overall goal is to bridge the results relating to the activation of MSCs that is specific for ultrasound with the current knowledge in molecular structure and the available physiological evidence that may have facilitated such phenomena. We discussed how collating the information revealed by available scientific investigations helps in the design of a more effective stimulus device for the proposed translational purposes. Traditionally, studies on the effects of ultrasound have focused largely on its mechanical and physical interaction with the targeted tissue through thermal-based therapies as well as non-thermal mechanisms including ultrasonic cavitation; gas body activation; the direct action of the compressional, tensile and shear stresses; radiation force; and acoustic streaming. However, the current review explores and attempts to establish whether the application of low-intensity ultrasound may be associated with the activation of specific MSCs, which in turn triggers relevant cell signaling as its molecular mechanism in achieving the desired therapeutic effects. Non-invasive brain stimulation has recently become an area of intense research interest for rehabilitation, and the implication of low-intensity ultrasound is particularly critical given the need to minimize heat generation to preserve tissue integrity for such applications.

Effectiveness, Compliance, and Safety of Dextrose Prolotherapy for Knee Osteoarthritis: A Meta-Analysis and Metaregression of Randomized Controlled Trials

OBJECTIVES

This study assessed the effectiveness, compliance, and safety of dextrose prolotherapy for patients with knee osteoarthritis.

DATA SOURCES

PubMed, EMBASE, the Cochrane Library Database, and the Scopus database from their inception to December 31, 2021.

METHODS

This study was conducted in accordance with the guidelines recommended by the Preferred Reporting Items for Systematic Reviews and Meta-Analysis. Randomized controlled trials regarding the effectiveness of dextrose prolotherapy in knee osteoarthritis were identified. The included trials were subjected to meta-analysis. Risk of bias was assessed using the Cochrane risk of bias tool. Subgroup and random-effects metaregression analyses were performed to explore any heterogeneity (I²) of treatment effects across studies.

RESULTS

A total of 14 trials enrolling 978 patients were included in the meta-analysis. Compared with placebo injection and noninvasive control therapy, dextrose prolotherapy had favorable effects on pain, global function, and quality of life during the overall follow-up. Dextrose prolotherapy yielded greater reductions in pain score over each follow-up duration than did the placebo. Compared with other invasive therapies, dextrose prolotherapy generally achieved comparable effects on pain and functional outcomes for each follow-up duration.Subgroup results indicated that combined intra-articular and extra-articular injection techniques may have stronger effects on pain than a single intra-articular technique.

CONCLUSIONS

Dextrose prolotherapy may have dose-dependent and time-dependent effects on pain reduction and function recovery, respectively, in patients with knee osteoarthritis. Due to remarkable heterogeneity and the risk of biases across the included trials, the study results should be cautiously interpreted.

Ultrasound-Guided Nerve Hydrodissection With 5% Dextrose 4 Weeks After Steroid Injection in Treatment of Carpal Tunnel Syndrome: A Retrospective Study

Objective

To investigate the efficacy and safety of ultrasound-guided nerve hydrodissection (HD) with 5% dextrose (D5W) as add-on therapy after corticosteroid injection in carpal tunnel syndrome (CTS), and provide a novel strategy.

Methods

In this retrospective study, patients with CTS who received ultrasound-guided nerve HD with D5W as add-on therapy after corticosteroid injection (combination group) were enrolled. Patients who received corticosteroid injection without add-on therapy (steroid group) were recruited as the control group. Ultrasound-guided nerve HD with D5W was performed 4 weeks after corticosteroid injection. Treatment effectiveness were assessed by visual analog scale (VAS) and Boston Carpal Tunnel Syndrome Questionnaire (BCTQ). The assessment was performed at baseline and 4, 8, and 12 weeks after corticosteroid injection. In addition, adverse events were recorded in this study.

Results

A total of 49 patients and 62 wrists meeting the criteria were included, with 24 patients and 31 wrists in the steroid group and 25 patients and 31 wrists in the combination group. Compared with baseline data, both groups showed greater improvement in VAS, BCTQs (BCTQ severity), and BCTQf (BCTQ function) at 4, 8, and 12 weeks follow-up. VAS, BCTQs, and BCTQf scores at baseline and week 4 were comparable between steroid group and combination group. Compared with steroid group, combination group exhibited a significant reduction in VAS, BCTQs, and BCTQf at 8- and 12-week follow-up (P ≤ 0.01). No adverse event occurred in any group.

Conclusions

Our results showed that ultrasound-guided nerve HD with D5W as add-on therapy after corticosteroid injection was efficacious and safe in CTS, and combination therapy is more beneficial than corticosteroid monotherapy in the improvement of symptoms and function at 8- and 12-week follow-up.

The effectiveness of dextrose prolotherapy in plantar fasciitis: A systemic review and meta-analysis

BACKGROUND

Dextrose prolotherapy (DPT) is considered to be a type of regenerative therapy and is widely used in various musculoskeletal disorders. Plantar fasciitis is a common cause of heel pain that affects the quality of life of many people. We aimed to evaluate the effectiveness and safety of DPT for plantar fasciitis.

METHODS

PubMed, Embase, and the Cochrane Library were searched from their respective inception dates to June 2021. Only randomized controlled trials comparing DPT and other interventions for plantar fasciitis were included in this review. Standardized mean differences (SMDs) with 95% confidence intervals were calculated for comparison. The outcome measurements included visual analog score, numeric rating scale, Foot Function index, Revised Foot Function index, American Orthopedic Foot and Ankle Score, and plantar fascia thickness. Post-treatment duration was classified as short-term (1-2 months), medium-term (3 months), or long-term (6 months).

RESULTS

Six studies with 388 adult patients diagnosed with plantar fasciitis were included for the meta-analysis. In terms of pain scores improvement, DPT was superior to placebo or exercise in the short-term (SMD: -1.163, 95%CI: -2.17 to -0.156) and the medium-term (SMD: -1.394, 95%CI: -2.702 to -0.085). DPT was inferior to corticosteroid injection in the short-term (SMD: 0.781, 95%CI: 0.41 to 1.152). For functional improvement, DPT was superior to placebo or exercise in the short-term (SMD: -1.51, 95%CI: -2.96 to -0.059), but inferior to corticosteroid injection (SMD: 0.526, 95%CI: 0.161 to 0.89) and extracorporeal shock wave therapy in the short-term (SMD: 0.484, 95%CI: 0.145 to 0.822). Randomized controlled trials showed a better pain improvement in the long-term for patients treated with DPT compared to corticosteroid (P = .002) and exercise control (P < .05). No significant differences were found between patients treated with DPT and patients treated with platelet-rich plasma.

CONCLUSION

Dextrose prolotherapy was a safe and effective treatment option for plantar fasciitis that may have long-term benefits for patients. The effects were comparable to extracorporeal shock wave therapy or platelet-rich plasma injection. Further studies with standardized protocols and long-term follow-up are needed to address potential biases.

Efficacy of 5% Dextrose Water Injection for Peripheral Entrapment Neuropathy: A Narrative Review

Current non-surgical treatment for peripheral entrapment neuropathy is considered insignificant and unsustainable; thus, it is essential to find an alternative novel treatment. The technique of perineural injection therapy using 5% dextrose water has been progressively used to treat many peripheral entrapment neuropathies and has been proven to have outstanding effects in a few high-quality studies. Currently, the twentieth edition of Harrison’s Principles of Internal Medicine textbook recommends this novel injection therapy as an alternative local treatment for carpal tunnel syndrome (CTS). Hence, this novel approach has become the mainstream method for treating CTS, and other studies have revealed its clinical benefit for other peripheral entrapment neuropathies. In this narrative review, we aimed to provide an insight into this treatment method and summarize the current studies on cases of peripheral entrapment neuropathy treated by this method.

ASIC1a is required for neuronal activation via low-intensity ultrasound stimulation in mouse brain

Accumulating evidence has shown transcranial low-intensity ultrasound can be potentially a non-invasive neural modulation tool to treat brain diseases. However, the underlying mechanism remains elusive and the majority of studies on animal models applying rather high-intensity ultrasound that cannot be safely used in humans. Here, we showed low-intensity ultrasound was able to activate neurons in the mouse brain and repeated ultrasound stimulation resulted in adult neurogenesis in specific brain regions. In vitro calcium imaging studies showed that a specific ultrasound stimulation mode, which combined with both ultrasound-induced pressure and acoustic streaming mechanotransduction, is required to activate cultured cortical neurons. ASIC1a and cytoskeletal proteins were involved in the low-intensity ultrasound-mediated mechanotransduction and cultured neuron activation, which was inhibited by ASIC1a blockade and cytoskeleton-modified agents. In contrast, the inhibition of mechanical-sensitive channels involved in bilayer-model mechanotransduction like Piezo or TRP proteins did not repress the ultrasound-mediated neuronal activation as efficiently. The ASIC1a-mediated ultrasound effects in mouse brain such as immediate response of ERK phosphorylation and DCX marked neurogenesis were statistically significantly compromised by ASIC1a gene deletion. Collated data suggest that ASIC1a is the molecular determinant involved in the mechano-signaling of low-intensity ultrasound that modulates neural activation in mouse brain.