Time-shifted co-administration of sub-analgesic doses of ambroxol and pregabalin attenuates oxaliplatin-induced cold allodynia in mice

Parthenolide as a potential analgesic in the treatment of paclitaxel-induced neuropathic pain: the rat modeling

In this study, we determined the therapeutic effect of parthenolide (PTL), the active component of Tanacetum parthenium, on neuropathic pain caused by paclitaxel (PTX), a chemotherapeutic drug frequently used in cancer treatment, at the gene and protein levels. To this end, 6 groups were formed: control, PTX, sham, 1 mg/PTL, 2 mg/kg PTL, and 4 mg/kg PTL. Pain formation was tested by Randall-Selitto analgesiometry and locomotor activity behavioral analysis. Then, PTL treatment was performed for 14 days. After the last dose of PTL was taken, Hcn2, Trpa1, Scn9a, and Kcns1 gene expressions were measured in rat brain (cerebral cortex/CTX) tissues. In addition, changes in the levels of SCN9A and KCNS1 proteins were determined by immunohistochemical analysis. Histopathological hematoxylin-eosin staining was also performed to investigate the effect of PTL in treating tissue damage on neuropathic pain caused by PTX treatment. When the obtained data were analyzed, pain threshold and locomotor activity decreased in PTX and sham groups and increased with PTL treatment. In addition, it was observed that the expression of the Hcn2, Trpa1, and Scn9a genes decreased while the Kcns1 gene expression increased. When protein levels were examined, it was determined that SCN9A protein expression decreased and the KCNS1 protein level increased. It was determined that PTL treatment also improved PTX-induced tissue damage. The results of this study demonstrate that non-opioid PTL is an effective therapeutic agent in the treatment of chemotherapy-induced neuropathic pain, especially when used at a dose of 4 mg/kg acting on sodium and potassium channels.

Novel Drug Targets and Emerging Pharmacotherapies in Neuropathic Pain

Neuropathic pain is a debilitating condition characterized by abnormal signaling within the nervous system, resulting in persistent and often intense sensations of pain. It can arise from various causes, including traumatic nerve injury, neuropathy, and certain diseases. We present an overview of current and emerging pharmacotherapies for neuropathic pain, focusing on novel drug targets and potential therapeutic agents. Current pharmacotherapies, including tricyclic antidepressants, gabapentinoids, and serotonin norepinephrine re-uptake inhibitors, are discussed, as are emerging treatments, such as ambroxol, cannabidiol, and N-acetyl-L-cysteine. Additionally, the article highlights the need for further research in this field to identify new targets and develop more effective and targeted therapies for neuropathic pain management.

Novel GPR18 Ligands in Rodent Pharmacological Tests: Effects on Mood, Pain, and Eating Disorders

The lack of selective pharmacological tools has limited the full unraveling of G protein-coupled receptor 18 (GPR18) functions. The present study was aimed at discovering the activities of three novel preferential or selective GPR18 ligands, one agonist (PSB-KK-1415) and two antagonists (PSB-CB-5 and PSB-CB-27). We investigated these ligands in several screening tests, considering the relationship between GPR18 and the cannabinoid (CB) receptor system, and the control of endoCB signaling over emotions, food intake, pain sensation, and thermoregulation. We also assessed whether the novel compounds could modulate the subjective effects evoked by Δ⁹-tetrahydrocannabinol (THC). Male mice or rats were pretreated with the GPR18 ligands, and locomotor activity, depression- and anxiety-like symptoms, pain threshold, core temperature, food intake, and THC-vehicle discrimination were measured. Our screening analyses indicated that GPR18 activation partly results in effects that are similar to those of CB receptor activation, considering the impact on emotional behavior, food intake, and pain activity. Thus, the orphan GPR18 may provide a novel therapeutic target for mood, pain, and/or eating disorders, and further investigation is warranted to better discern its function.

Ambroxol for neuropathic pain: hiding in plain sight?

ABSTRACT

Ambroxol is a multifaceted drug with primarily mucoactive and secretolytic actions, along with anti-inflammatory, antioxidant, and local anaesthetic properties. It has a long history of use in the treatment of respiratory tract diseases and has shown to be efficacious in relieving sore throat. In more recent years, ambroxol has gained interest for its potential usefulness in treating neuropathic pain. Research into this area has been slow, despite clear preclinical evidence to support its primary analgesic mechanism of action-blockade of voltage-gated sodium (Na v ) channels in sensory neurons. Ambroxol is a commercially available inhibitor of Na v 1.8, a crucial player in the pathophysiology of neuropathic pain, and Na v 1.7, a particularly exciting target for the treatment of chronic pain. In this review, we discuss the analgesic mechanisms of action of ambroxol, as well as proposed synergistic properties, followed by the preclinical and clinical results of its use in the treatment of persistent pain and neuropathic pain symptoms, including trigeminal neuralgia, fibromyalgia, and complex regional pain syndrome. With its well-established safety profile, extensive preclinical and clinical drug data, and early evidence of clinical effectiveness, ambroxol is an old drug worthy of further investigation for repurposing. As a patent-expired drug, a push is needed to progress the drug to clinical trials for neuropathic pain. We encourage the pharmaceutical industry to look at patented drug formulations and take an active role in bringing an optimized version for neuropathic pain to market.

Targeting strategies for oxaliplatin-induced peripheral neuropathy: clinical syndrome, molecular basis, and drug development

Oxaliplatin (OHP)-induced peripheral neurotoxicity (OIPN) is a severe clinical problem and potentially permanent side effect of cancer treatment. For the management of OIPN, accurate diagnosis and understanding of significant risk factors including genetic vulnerability are essential to improve knowledge regarding the prevalence and incidence of OIPN as well as enhance strategies for the prevention and treatment of OIPN. The molecular mechanisms underlying OIPN are complex, with multi-targets and various cells causing neuropathy. Furthermore, mechanisms of OIPN can reinforce each other, and combination therapies may be required for effective management. However, despite intense investigation in preclinical and clinical studies, no preventive therapies have shown significant clinical efficacy, and the established treatment for painful OIPN is limited. Duloxetine is the only agent currently recommended by the American Society of Clinical Oncology. The present article summarizes the most recent advances in the field of studies on OIPN, the overview of the clinical syndrome, molecular basis, therapy development, and outlook of future drug candidates. Importantly, closer links between clinical pain management teams and oncology will advance the effectiveness of OIPN treatment, and the continued close collaboration between preclinical and clinical research will facilitate the development of novel prevention and treatments for OIPN.

Novel Functionalized Amino Acids as Inhibitors of GABA Transporters with Analgesic Activity

Neuropathic pain resistance to pharmacotherapy has encouraged researchers to develop effective therapies for its treatment. γ-Aminobutyric acid (GABA) transporters 1 and 4 (mGAT1 and mGAT4) have been increasingly recognized as promising drug targets for neuropathic pain (NP) associated with imbalances in inhibitory neurotransmission. In this context, we designed and synthesized new functionalized amino acids as inhibitors of GABA uptake and assessed their activities toward all four mouse GAT subtypes (mGAT1–4). According to the obtained results, compounds 2RS,4RS-39c (pIC₅₀ (mGAT4) = 5.36), 50a (pIC₅₀ (mGAT2) = 5.43), and 56a (with moderate subtype selectivity that favored mGAT4, pIC₅₀ (mGAT4) = 5.04) were of particular interest and were therefore evaluated for their cytotoxic and hepatotoxic effects. In a set of in vivo experiments, both compounds 50a and 56a showed antinociceptive properties in three rodent models of NP, namely, chemotherapy-induced neuropathic pain models (the oxaliplatin model and the paclitaxel model) and the diabetic neuropathic pain model induced by streptozotocin; however compound 56a demonstrated predominant activity. Since impaired motor coordination is also observed in neuropathic pain conditions, we have pointed out that none of the test compounds induced motor deficits in the rotarod test.

Comparison of Bromhexine and its Active Metabolite - Ambroxol as Potential Analgesics Reducing Oxaliplatin-induced Neuropathic Pain - Pharmacodynamic and Molecular Docking Studies

BACKGROUND

Painful peripheral neuropathy is a dose-limiting adverse effect of the antitumor drug oxaliplatin. The main symptoms of neuropathy: tactile allodynia and cold hyperalgesia, appear in more than 80% of patients on oxaliplatin therapy and are due to the overexpression of neuronal sodium channels (Navs) and neuroinflammation.

OBJECTIVE

This study assessed antiallodynic and antihyperalgesic properties of two repurposed drugs with antiinflammatory and Nav-blocking properties (bromhexine and its pharmacologically active metabolite - ambroxol) in a mouse model of neuropathic pain induced by oxaliplatin. Using molecular docking techniques, we predicted targets implicated in the observed in vivo activity of bromhexine.

METHODS

Oxaliplatin (a single intraperitoneal dose of 10 mg/kg) induced tactile allodynia and cold hyperalgesia in CD-1 mice and the effectiveness of single-dose or repeated-dose bromhexine and ambroxol to attenuate pain hypersensitivity was assessed in von Frey and cold plate tests. Additionally, Veber analysis and molecular docking experiments of bromhexine on mouse (m) and human (h) Nav1.6-1.9 were carried out.

RESULTS

At the corresponding doses, ambroxol was more effective than bromhexine as an antiallodynic agent. However, at the dose of 150 mg/kg, ambroxol induced motor impairments in mice. Repeated-dose bromhexine and ambroxol partially attenuated the development of late-phase tactile allodynia in oxaliplatin-treated mice. Only 7-day administration of bromhexine attenuated the development of late-phase cold hyperalgesia. Bromhexine was predicted to be a strong inhibitor of mNav1.6, mNav1.7, mNav1.9, and hNav1.7-hNav1.9.

CONCLUSION

The conversion of bromhexine to other than ambroxol active metabolites should be considered when interpreting some of its in vivo effects. Nav-blocking properties of bromhexine (and previously also predicted for ambroxol) might underlie its ability to attenuate pain caused by oxaliplatin.

Chemotherapy-induced peripheral neuropathy: part 1-current state of knowledge and perspectives for pharmacotherapy

Background

Despite the increasing knowledge of the etiology of neuropathic pain, this type of chronic pain is resistant to available analgesics in approximately 50% of patients and therefore is continuously a subject of considerable interest for physiologists, neurologists, medicinal chemists, pharmacologists and others searching for more effective treatment options for this debilitating condition.

Materials and methods

The present review article is the first of the two articles focused on chemotherapy-induced peripheral neuropathy (CIPN).

Results

CIPN is regarded as one of the most common drug-induced neuropathies and is highly pharmacoresistant. The lack of efficacious pharmacological methods for treating CIPN and preventing its development makes CIPN-related neuropathic pain a serious therapeutic gap in current medicine and pharmacotherapy. In this paper, the most recent advances in the field of studies on CIPN caused by platinum compounds (namely oxaliplatin and cisplatin), taxanes, vinca alkaloids and bortezomib are summarized.

Conclusions

The prevalence of CIPN, potential causes, risk factors, symptoms and molecular mechanisms underlying this pharmacoresistant condition are discussed.

Graphic abstract

Dual-action ambroxol in treatment of chronic pain in Gaucher Disease

A significant number of patients with Gaucher disease (GD) suffer from chronic or acute pain that reduces their quality of life. A mutation in lysosomal enzyme β-glucosidase (GCase) leads to an accumulation of glucocerebroside in the macrophage-lineage cells, causing the development of clinical symptoms. Novel studies have revealed that ambroxol (trans-4-(2-amino-3,5-dibromobenzylamino)-cyclohexanol), the well-known mucolytic drug, acts as a chaperone for the mutant, misfolded enzyme. In addition, as has recently been shown, ambroxol is a Na_v 1.8 channel blocker in Aβ, Aδ and unmyelinated C fibres, and therefore reduces the transmission of sensory stimuli from the primary afferent neurons to the dorsal spinal cord. In this way, it can act analgetically. Thus, in addition to broncholytic properties, ambroxol combines two other important functions: it enhances enzyme replacement therapy (ERT) and pain management in patients with GD. We present a 38-year-old female patient with type 3 GD who had reported permanent bone pain in the lumbar-sacral part of the spine for over a year without any pathology evidenced in the undertaken, recommended diagnostic tests. The pain was partly controlled with standard analgesics, that is, paracetamol and tramadol. Ambroxol was introduced at a dose of 150mg/d without a noticeable effect. However, when the dose was increased up to 450mg/d, the intensity of pain diminished and subsided within the following months. Two of three attempts to reduce the dose of ambroxol resulted in a pain relapse within a week, which subsided after resetting the previous, higher dose. This observation of the effects of ambroxol in a GD patient is worth considering for other GD patients with chronic pain.

Chemotherapy-induced peripheral neuropathy-part 2: focus on the prevention of oxaliplatin-induced neurotoxicity

BACKGROUND

Chemotherapy-induced peripheral neuropathy (CIPN) is regarded as one of the most common dose-limiting adverse effects of several chemotherapeutic agents, such as platinum derivatives (oxaliplatin and cisplatin), taxanes, vinca alkaloids and bortezomib. CIPN affects more than 60% of patients receiving anticancer therapy and although it is a nonfatal condition, it significantly worsens patients' quality of life. The number of analgesic drugs used to relieve pain symptoms in CIPN is very limited and their efficacy in CIPN is significantly lower than that observed in other neuropathic pain types. Importantly, there are currently no recommended options for effective prevention of CIPN, and strong evidence for the utility and clinical efficacy of some previously tested preventive therapies is still limited.

METHODS

The present article is the second one in the two-part series of review articles focused on CIPN. It summarizes the most recent advances in the field of studies on CIPN caused by oxaliplatin, the third-generation platinum-based antitumor drug used to treat colorectal cancer. Pharmacological properties of oxaliplatin, genetic, molecular and clinical features of oxaliplatin-induced neuropathy are discussed.

RESULTS

Available therapies, as well as results from clinical trials assessing drug candidates for the prevention of oxaliplatin-induced neuropathy are summarized.

CONCLUSION

Emerging novel chemical structures-potential future preventative pharmacotherapies for CIPN caused by oxaliplatin are reported.

Searching for analgesic drug candidates alleviating oxaliplatin-induced cold hypersensitivity in mice

Oxaliplatin is a third-generation, platinum-based derivative used to treat advanced colorectal cancer. Within the patient population on oxaliplatin therapy, a lower incidence of hematological adverse effects and gastrointestinal toxicity is noted, but severe neuropathic pain episodes characterized by increased cold and tactile hypersensitivity are present in ~95% of patients. This drug is also used to induce a rodent model of chemotherapy-induced peripheral neuropathy (CIPN)-related neuropathic pain which is widely used in the search for novel therapies for CIPN prevention and treatment. This paper provides a step-by-step, detailed description of the prevention and intervention protocols used in our laboratory for the assessment of oxaliplatin-induced cold allodynia in mice. To establish cold sensitivity in mice, the cold plate test was used. Latencies to pain reaction in response to cold stimulus (2.5°C) for vehicle-treated non-neuropathic mice, vehicle-treated mice injected with oxaliplatin (neuropathic control), and oxaliplatin-treated mice treated additionally with duloxetine are compared. Duloxetine is a serotonin/noradrenaline reuptake inhibitor which was found to produce significant pain relief in patients with CIPN symptoms. In our present study, duloxetine administered intraperitoneally at the dose of 30 mg/kg served as a model antiallodynic drug which attenuated or partially prevented cold allodynia caused by oxaliplatin.

Topical Ambroxol 20% for the Treatment of Classical Trigeminal Neuralgia - A New Option? Initial Clinical Case Observations

BACKGROUND

Trigeminal neuralgia is difficult to treat and shows upregulation of sodium channels. The expectorant ambroxol acts as a strong local anesthetic, about 40 times stronger than lidocaine. It preferentially inhibits the channel subtype Na_v 1.8, expressed especially in nociceptive C-fibers. It seemed reasonable to try ambroxol for the treatment with neuropathic facial pain unresponsive to other standard options.

MATERIAL AND METHODS

Medical records of patients suffering from classical trigeminal neuralgia (n = 5) and successful pain reduction following topical ambroxol 20% cream in addition to standard treatment are reported.

RESULTS

All patients reported pain attacks with pain intensity between 4 and 10 NRS (numeric pain scale). In all cases they could be triggered, 3 patients reported additional spontaneous pain. Attacks were reduced in all 5 patients. Pain reduction achieved following ambroxol 20% cream was 2-8 points (NRS) earliest within 15-30 minutes and lasted for 4-6 hours mostly. This was reproducible in all cases; in one case pain was eliminated after 1 week. No patient reported side effects or skin changes; oral medication was reduced in 2 patients.

CONCLUSION

For the first time, a clinically significant pain relief following topical ambroxol 20% cream in patients with trigeminal neuralgia is reported. In view of the positive side effect profile, topical ambroxol for patients with such a highly impaired quality of life should be investigated further as a matter of urgency.

Interventional and preventive effects of aripiprazole and ceftriaxone used alone or in combination on oxaliplatin-induced tactile and cold allodynia in mice

BACKGROUND AND PURPOSE

Chemotherapy-induced peripheral neuropathy (CIPN) is a pharmacoresistant neurological complication induced by some antitumor drugs. This study aimed to assess antiallodynic properties of aripiprazole and ceftriaxone used alone or in combination to attenuate neuropathic pain related to CIPN caused by oxaliplatin.

METHODS

Neuropathic pain was induced in mice by a single intraperitoneal dose of oxaliplatin (10 mg/kg). Aripiprazole and ceftriaxone were used in a single- or repeated dosing protocol. Their antiallodynic activity was assessed using von Frey and cold plate tests on the day of oxaliplatin injection and after 7 days. The influence of aripiprazole and ceftriaxone on animals' locomotor activity and motor coordination was also assessed.

RESULTS

Single-dose and repeated-dose aripiprazole 10 mg/kg and ceftriaxone 200 mg/kg used alone and in combination attenuated early-phase and late-phase tactile allodynia in oxaliplatin-treated mice. Repeated administrations of ceftriaxone 200 mg/kg prevented the development of late-phase tactile allodynia. Both drugs showed no antiallodynic properties in the cold plate test. Single-dose aripiprazole 1 and 10 mg/kg but not its repeated administration significantly decreased locomotor activity of oxaliplatin-treated mice. Single-dose aripiprazole 1 and 10 mg/kg, aripiprazole 1 mg/kg + ceftriaxone 50 mg/kg and aripiprazole 1 mg/kg + ceftriaxone 200 mg/kg impaired motor coordination in the rotarod test.

CONCLUSIONS

In mice, neither ceftriaxone nor aripiprazole attenuated cold allodynia. Ceftriaxone alone could attenuate tactile allodynia caused by oxaliplatin without inducing motor adverse effects. Although the administration of aripiprazole reduced tactile allodynia, this effect seems to be limited considering severe motor deficits induced by this drug.