Novel treatments for chronic pain: moving beyond opioids

Phenylpropanoid-enriched broccoli seedling extract can reduce inflammatory markers and pain behavior

BACKGROUND

Pain is a worldwide problem requiring an effective, affordable, non-addictive therapy. Using the edible plant broccoli, a growth protocol was developed to induce a concentrated combinatorial of potential anti-inflammatories in seedlings.

METHODS

A growth method was utilized to produce a phenylpropanoid-rich broccoli sprout extract, referred to as Original Extract (OE). OE was concentrated and then resuspended for study of the effects on inflammation events. A rabbit disc model of inflammation and degeneration, and, a mouse model of pain behavior were used for in vivo and in vitro tests. To address aspects of mammalian metabolic processing, the OE was treated with the S9 liver microsome fraction derived from mouse, for use in a mouse in vivo study. Analytical chemistry was performed to identify major chemical species. Continuous variables were analyzed with a number of methods including ANOVA, and two-tailed t tests, as appropriate.

RESULTS

In a rabbit spine (disc) injury model, inflammatory markers were reduced, and levels of regenerative markers were increased as a result of OE treatment, both in vivo and in vitro. In a mouse pain behavioral model, after treatment with S9 liver microsome fraction, the resultant extract significantly reduced early and late pain behavior in response to a pain stimulus. The OE itself reduced pain behavior in the mouse pain model, but did not achieve the level of significance observed for S9-treated extract. Analytical chemistry undertaken on the extract constituents revealed identities of the chemical species in OE, and how S9 liver microsome fraction treatment altered species identities and proportions.

CONCLUSIONS

In vitro and in vivo results indicate that the OE, and S9-treated OE broccoli extracts are worthwhile materials to develop a non-opiate inflammation and pain-reducing treatment.

Long-range action of an HDAC inhibitor treats chronic pain in a spared nerve injury rat model

Histone deacetylase inhibitors (HDACi) that modulate epigenetic regulation and are approved for treating rare cancers have, in disease models, also been shown to mitigate neurological conditions, including chronic pain. They are of interest as non-opioid treatments, but achieving long-term efficacy with limited dosing has remained elusive. Here we utilize a triple combination formulation (TCF) comprised of a pan-HDACi vorinostat (Vo at its FDA-approved daily dose of 50mg/Kg), the caging agent 2-hydroxypropyl-β-cyclodextrin (HPBCD) and polyethylene glycol (PEG) known to boost plasma and brain exposure and efficacy of Vo in mice and rats, of various ages, spared nerve injury (SNI) model of chronic neuropathic pain. Administration of the TCF (but not HPBCD and PEG) decreased mechanical allodynia for 4 weeks without antagonizing weight, anxiety, or mobility. This was achieved at less than 1% of the total dose of Vo approved for 4 weeks of tumor treatment and associated with decreased levels of major inflammatory markers and microglia in ipsilateral (but not contralateral) spinal cord regions. A single TCF injection was sufficient for 3-4 weeks of efficacy: this was mirrored in repeat injections, specific for the injured paw and not seen on sham treatment. Pharmacodynamics in an SNI mouse model suggested pain relief was sustained for days to weeks after Vo elimination. Doubling Vo in a single TCF injection proved effectiveness was limited to male rats, where the response amplitude tripled and remained effective for > 2 months, an efficacy that outperforms all currently available chronic pain pharmacotherapies. Together, these data suggest that through pharmacological modulation of Vo, the TCF enables single-dose effectiveness with extended action, reduces long-term HDACi dosage, and presents excellent potential to develop as a non-opioid treatment option for chronic pain.

Thalamocortical Mechanisms Underlying Real and Imagined Acupuncture

Both acupuncture and imagery have shown potential for chronic pain management. However, the mechanisms underlying their analgesic effects remain unclear. This study aims to explore the thalamocortical mechanisms underlying acupuncture and video-guided acupuncture imagery treatment (VGAIT), a combination of acupuncture and guided imagery, using the resting-state functional connectivity (rsFC) of three thalamic subdivisions-the ventral posterolateral thalamus (VPL), mediodorsal thalamus (MD), and motor thalamus subregion (Mthal)-associated with somatosensory, limbic, and motor circuity. Twenty-seven healthy individuals participated in a within-subject randomized crossover design study. Results showed that compared to sham acupuncture, real acupuncture altered the rsFC between the thalamus and default mode network (DMN) (i.e., mPFC, PCC, and precuneus), as well as the prefrontal and somatosensory cortex (SI/SII). Compared to the VGAIT control, VGAIT demonstrated greater rsFC between the thalamus and key nodes within the interoceptive network (i.e., anterior insula, ACC, PFC, and SI/SII), as well as the motor and sensory cortices (i.e., M1, SMA, and temporal/occipital cortices). Furthermore, compared to real acupuncture, VGAIT demonstrated increased rsFC between the thalamus (VPL/MD/Mthal) and task-positive network (TPN). Further correlations between differences in rsFC and changes in the heat or pressure pain threshold were also observed. These findings suggest that both acupuncture- and VGAIT-induced analgesia are associated with thalamocortical networks. Elucidating the underlying mechanism of VGAIT and acupuncture may facilitate their development, particularly VGAIT, which may be used as a potential remote-delivered pain management approach.

Paediatric pain management: from regional to virtual

PURPOSE OF REVIEW

Due to increased interest in opioid-sparing multimodal analgesic strategies both inside and outside of the operating room, anaesthesiologists have started to look towards regional anaesthesia as well as nonpharmacological pain-reducing techniques. The purpose of this article is to discuss current trends and recent developments in regional anaesthesia and virtual reality for paediatric pain management.

RECENT FINDINGS

The development of novel fascial plane blocks has expanded regional options for anaesthesiologists, especially when neuraxial anaesthesia is not a viable or straightforward option. Other regional techniques, such as spinal anaesthesia and continuous epidural analgesia for infants and neonates, are becoming more popular, as more paediatric anaesthesiologists become familiar with these techniques. Virtual reality for paediatric pain management is a relatively new area of study that has shown promise, but more research needs to be done before widespread adoption of this practice becomes a reality. Various preexisting pain-reducing strategies such as distraction and biofeedback are being integrated with virtual reality to help optimize its effect on pain and anxiety for paediatric patients.

SUMMARY

Regional anaesthesia and virtual reality are valuable tools that serve to alleviate pain in paediatric patients. Advances are being made within both fields in various healthcare settings for different types of pain. Over the next few years, they will likely both play an increasing role in paediatric pain management.

Inflammation and histone modification in chronic pain

Increasing evidence suggests that epigenetic mechanisms have great potential in the field of pain. The changes and roles of epigenetics of the spinal cord and dorsal root ganglia in the chronic pain process may provide broad insights for future pain management. Pro-inflammatory cytokines and chemokines released by microglia and astrocytes, as well as blood-derived macrophages, play critical roles in inducing and maintaining chronic pain, while histone modifications may play an important role in inflammatory metabolism. This review provides an overview of neuroinflammation and chronic pain, and we systematically discuss the regulation of neuroinflammation and histone modifications in the context of chronic pain. Specifically, we analyzed the role of epigenetics in alleviating or exacerbating chronic pain by modulating microglia, astrocytes, and the proinflammatory mediators they release. This review aimed to contribute to the discovery of new therapeutic targets for chronic pain.

Discovery of a novel class of benzoxazole derivatives as histamine H3 receptor ligands for the treatment of neuropathic pain

To discover effective analgesics, we summarize the synthesis, optimization, and pharmacological anti-nociceptive effects of a novel series of benzoxazole derivatives targeting H₃ receptor (H₃R). The new benzoxazoles were assayed in vitro for histamine H₃R and H₁R binding affinity. The best compound 8d (2-methyl-6-(3-(4-methylpiperazin-1-yl)propoxy)benzo[d]oxazole) exhibited high affinity for H₃R (K_i = 19.7 nM), high selectivity for ten other off-target receptors, and negligible effects on human ether-a-go-go-related gene (hERG, cardiac ion channel). In rodent animals, compound 8d dose-dependently reversed formalin-evoked pain (Phase I, ED₅₀ = 6.0 mg/kg; Phase II, ED₅₀ = 7.8 mg/kg) and CCI-induced neuropathic pain (chronic constriction injury, ED₅₀ = 15.6 mg/kg). Furthermore, compound 8d showed an excellent safety profile in acute toxicity test (LD₅₀ > 2000 mg/kg) with a therapeutic index (TI = LD₅₀/ED₅₀) > 250 and showed a desirable drug-like pharmacokinetic profile. Above characteristics indicate that compound 8d represents a promising candidate analgesic for the treatment of neuropathic pain.

Molecular monitoring of patient response to painkiller drugs

INTRODUCTION

Non-steroidal anti-inflammatory drugs and opioids are widely prescribed for the treatment of mild to severe pain. Wide interindividual variability regarding the analgesic efficacy and adverse reactions to these drugs (ADRs) exist, although the mechanisms responsible for these ADRs are not well understood.

AREAS COVERED

We provide an overview of the clinical impact of variants in genes related to the pharmacokinetics and pharmacodynamics of painkillers, as well as those associated with the susceptibility to ADRs. Also, we discuss the current pharmacogenetic-guided treatment recommendations for the therapeutic use of non-steroidal anti-inflammatory drugs and opioids.

EXPERT OPINION

In the light of the data analyzed, common variants in genes involved in pharmacokinetics and pharmacodynamics processes may partially explain the lack of response to painkiller treatment and the occurrence of adverse drug reactions. The implementation of high-throughput sequencing technologies may help to unveil the role of rare variants as considerable contributors to explaining the interindividual variability in drug response. Furthermore, a consensus between the diverse pharmacogenetic guidelines is necessary to extend the implementation of pharmacogenetic-guided prescription in daily clinical practice. Additionally, the physiologically-based pharmacokinetics and pharmacodynamics modeling techniques may contribute to the improvement of these guidelines and facilitate clinicians drug dose adjustment.

The imidazodiazepine, KRM-II-81: An example of a newly emerging generation of GABAkines for neurological and psychiatric disorders

GABAkines, or positive allosteric modulators of γ-aminobutyric acid-A (GABA_A) receptors, are used for the treatment of anxiety, epilepsy, sleep, and other disorders. The search for improved GABAkines, with reduced safety liabilities (e.g., dependence) or side-effect profiles (e.g., sedation) constituted multiple discovery and development campaigns that involved a multitude of strategies over the past century. Due to the general lack of success in the development of new GABAkines, there had been a decades-long draught in bringing new GABAkines to market. Recently, however, there has been a resurgence of efforts to bring GABAkines to patients, the FDA approval of the neuroactive steroid brexanolone for post-partum depression in 2019 being the first. Other neuroactive steroids are in various stages of clinical development (ganaxolone, zuranolone, LYT-300, Sage-324, PRAX 114, and ETX-155). These GABAkines and non-steroid compounds (GRX-917, a TSPO binding site ligand), darigabat (CVL-865), an α2/3/5-preferring GABAkine, SAN711, an α3-preferring GABAkine, and the α2/3-preferring GABAkine, KRM-II-81, bring new therapeutic promise to this highly utilized medicinal target in neurology and psychiatry. Herein, we also discuss possible conditions that have enabled the transition to a new age of GABAkines. We highlight the pharmacology of KRM-II-81 that has the most preclinical data reported. KRM-II-81 is the lead compound in a new series of orally bioavailable imidazodiazepines entering IND-enabling safety studies. KRM-II-81 has a preclinical profile predicting efficacy against pharmacoresistant epilepsies, traumatic brain injury, and neuropathic pain. KRM-II-81 also produces anxiolytic- and antidepressant-like effects in rodent models. Other key features of the pharmacology of this compound are its low sedation rate, lack of tolerance development, and the ability to prevent the development of seizure sensitization.

Endogenous Expression of G-CSF in Rat Dorsal Root Ganglion Neurons after Nerve Injury

Granulocyte colony-stimulating factor (G-CSF) has been reported to modulate pain function following nerve injury. However, the expression of endogenous G-CSF in the dorsal root ganglion (DRG) and the response to nerve injury remain unclear. In the present study, we demonstrated that G-CSF and G-CSFR are mainly expressed in both small- and medium-diameter DRG neurons in rats and are responsible for transmitting pain responses. G-CSF and G-CSFR were co-expressed in certain nociceptive DRG neurons. In addition, G-CSF was expressed in satellite glial cells around large-diameter DRG neurons. After sciatic nerve injury, the number of G-CSF-positive DRG neurons was increased in both the ipsilateral and contralateral lesion sites in rats. However, G-CSF expression in satellite glial cells was not affected by nerve injury. To clarify the role of G-CSF in pain, exogenous G-CSF was administered to a rat model of neuropathic pain induced by partial sciatic nerve transaction (PST). Our results indicate that treatment with G-CSF did not attenuate but exacerbated neuropathic pain. In summary, G-CSF may directly activate sensory neurons and contribute to nociceptive signaling.