Involvement of central mu-opioid system in the scratching behavior in mice, and the suppression of it by the activation of kappa-opioid system

Randomized controlled trial of nalfurafine for refractory pruritus in hemodialysis patients

Background: Chronic kidney disease-associated pruritus (CKD-aP) is very common and sometimes refractory to treatment in hemodialysis patients. In a trial conducted in Japan, nalfurafine, effectively reduced itching of treatment-resistant CKD-aP. Our present bridging study aimed to evaluate the efficacy and safety of nalfurafine in Chinese cohort with refractory CKD-aP.Methods: In this phase III, multicenter bridging study conducted at 22 sites in China, 141 Chinese cases with refractory CKD-aP were randomly (2:2:1) assigned to receive 5 μg, 2.5 μg of nalfurafine or a placebo orally for 14 days in a double-blind manner. The primary end point was the mean decrease in the mean visual analogue scale (VAS) from baseline.Results: A total of 141 patients were included. The primary endpoint analysis based on full analysis set (FAS), the difference of mean VAS decrease between 5 μg nalfurafine and placebo group was 11.37 mm (p = .041); the difference of mean VAS decrease between 2.5 μg and placebo group was 8.81 mm, but not statistically significantly different. Both differences were greater than 4.13 mm, which met its predefined success criterion of at least 50% efficacy of the key Japanese clinical trial. The per protocol set (PPS) analysis got similar results. The incidence of adverse drug reactions (ADRs) was 49.1% in 5μg, 38.6% in 2.5 μg and 33.3% in placebo group. The most common ADR was insomnia, seen in 21 of the 114 nalfurafine patients.Conclusions: Oral nalfurafine effectively reduced itching with few significant ADRs in Chinese hemodialysis patients with refractory pruritus.

Endogenous Opioid Imbalance as a Potential Factor Involved in the Pathogenesis of Chronic Kidney Disease-Associated Pruritus in Dialysis Patients

Chronic pruritus is one of the most common symptoms of dermatological diseases. It may occur in the course of other disorders, such as kidney disease. Chronic kidney disease-associated pruritus (CKD-aP) most often affects people with end-stage renal disease. The etiology of this condition is still not fully understood, but researchers are currently focusing on a thorough analysis of the association between disturbed opioid balance and increased neuronal signaling leading to pruritus. The aim of this study is to assess the concentration of endogenous opioids in dialysis patients with and without pruritus and in the control group, and to determine the correlation between the concentration of these substances and the occurrence and severity of itching. The study involved 126 dialysis patients and 50 healthy controls. Patients were divided into groups with pruritus (n = 62) and without pruritus (n = 64). The severity of pruritus was assessed using the NRS scale. The concentration of endogenous opioids was determined using the ELISA. The concentration of met-enkephalin was higher in the group of patients with pruritus compared to the control group. Moreover, significantly lower levels of β-endorphin and dynorphin A were observed in the group of dialysis patients compared to the control group. In addition, a statistically significant difference was seen between the β-endorphin concentration in the group of dialysis patients with pruritus compared to the group without pruritus. The ratio of β-endorphin/dynorphin A concentrations was significantly lower in the group of patients with pruritus compared to patients without pruritus and the control group. No correlations were found between serum level of studied opioids and the severity of pruritus. The concentrations of the studied opioids did not correlate with the severity of pruritus. Observed opioid imbalance may affect the occurrence of CKD-aP in dialysis patients, but a thorough understanding of the mechanism of action of these substances in the sensation of pruritus is necessary to assess the possibility of finding a new therapeutic target.

Uremic pruritus: pathophysiology, clinical presentation, and treatments

Uremic pruritus is one of the most common and bothersome symptoms in patients with end-stage renal disease. Most patients with uremic pruritus experience a prolonged and relapsing course and significant impairments of quality of life. The pathophysiology of uremic pruritus is not completely understood. A complex interplay among cutaneous biology and the nervous and immune systems has been implicated, with the involvement of various inflammatory mediators, neurotransmitters, and opioids. Uremic pruritus treatment outcomes are often unsatisfactory. Clinical trials have mostly been small in scale and have reported inconsistent results. Recent evidence shows that gabapentinoids, nalfurafine, and difelikefalin are effective for relieving uremic pruritus in hemodialysis patients. This review provides an overview of the epidemiology and proposed mechanisms of uremic pruritus, then highlights the manifestations of and clinical approach to uremic pruritus. Current evidence regarding treatment options, including topical treatments, treatment of underlying disease, phototherapy, and systemic treatments, is also outlined. With a better understanding of uremic pruritus, more therapeutic options can be expected in the near future.

The Kappa Opioid Receptor: A Promising Therapeutic Target for Multiple Pathologies

Kappa-opioid receptors (KOR) are widely expressed throughout the central nervous system, where they modulate a range of physiological processes depending on their location, including stress, mood, reward, pain, inflammation, and remyelination. However, clinical use of KOR agonists is limited by adverse effects such as dysphoria, aversion, and sedation. Within the drug-development field KOR agonists have been extensively investigated for the treatment of many centrally mediated nociceptive disorders including pruritis and pain. KOR agonists are potential alternatives to mu-opioid receptor (MOR) agonists for the treatment of pain due to their anti-nociceptive effects, lack of abuse potential, and reduced respiratory depressive effects, however, dysphoric side-effects have limited their widespread clinical use. Other diseases for which KOR agonists hold promising therapeutic potential include pruritis, multiple sclerosis, Alzheimer’s disease, inflammatory diseases, gastrointestinal diseases, cancer, and ischemia. This review highlights recent drug-development efforts targeting KOR, including the development of G-protein–biased ligands, mixed opioid agonists, and peripherally restricted ligands to reduce side-effects. We also highlight the current KOR agonists that are in preclinical development or undergoing clinical trials.

Hypothalamic response with PKA/CREB signaling is associated with direct cerebroventricular administration of bombesin-induced scratching

Bombesin (BN) is an itch-specific mediator that causes intense itch-scratching activity in mammals. Although most examinations of BN-induced itch processing have focused on the spinal cord, the involvement of central nervous system mechanisms remains unclear. Here, we investigated how relationships among hypothalamic regions regulate BN-mediated itch-scratch processes. We found that intracerebroventricular (i.c.v.) administration of BN (0.04-4 μg) elicited intense itch scratching in mice, whereas BN (0.4-400 μg) administered via intravenous tail injection failed to evoke a scratching response. Additionally, nalfurafine had no significant effects on BN-induced scratching behavior, indicating that central modulation of BN is distinct from histamine-mediated histaminergic itch and chloroquine-mediated non-histaminergic itch signaling pathways. We labeled BN with a fluorescent tag, 7-nitrobenz-2-oxa-1 (NBD), and traced its fluorescence in the hypothalamus for 30 min following i.c.v. NBD-BN administration. Accordingly, we confirmed that i.c.v. administration of BN enhanced c-Fos expression in the dorsal medial nucleus of the hypothalamus, where neuromedin B receptors and gastrin-releasing peptide receptors are highly expressed. Interestingly, in situ injection of BN into the hypothalamus immediately and robustly induced itch-scratching behavior. Moreover, gene transcripts and western blot assay revealed that BN receptor-dependent PKA/CREB signaling was upregulated in the hypothalamus after i.c.v. administration of BN. Consistently, pretreatment with a PKA inhibitor, Rp-cAMP, significantly reduced BN-induced scratching behavior. Our results indicate that the dorsal medial nucleus of the hypothalamus may be a key nucleus in mediating BN-mediated itch and hypothalamic PKA/CREB signaling is involved in regulating BN-mediated itch.

Post-Marketing Surveillance Study of the Safety and Efficacy of Nalfurafine (Capsules 2.5 μg, Oral Dispersing Tablets 2.5 μg) in 1186 Patients with Chronic Liver Disease and Intractable Pruritus

Background

Nalfurafine (Remitch^®, Toray Industries, Inc.) is a selective κ-receptor agonist approved in Japan for the improvement of pruritus in patients with chronic liver diseases (only when existing treatments bring insufficient efficacy) in May 2015.

Methods

A post-marketing Specific Drug Use Survey was conducted in Japan (March 1, 2016 to June 30, 2020) of the safety and efficacy of nalfurafine for the improvement of pruritus in patients with chronic liver disease.

Results

Among 1186 cases analyzed for safety, the incidence of adverse drug reactions was 9.4% (112/1186 cases), lower than 61.4% reported in pre-marketing surveillance (297/484 cases). No specific safety issues were found and no cases of concern for drug dependence identified. Efficacy (itch improvement) was demonstrated in 73.16% (815/1114 cases; 12-week analysis set) and in 85.67% (520/607; general assessment of itch improvement at 1-year analysis set). A significant difference was found in 4 items of itch improvement at 12 weeks and 8 items of itch improvement at 1 year. No noteworthy issues were identified. Mean Visual Analog Scale (VAS) values after 12 weeks and 1 year after the first dose were significantly lower than the baseline (p < 0.0001 for both treatment durations). Mean severity scores (Kawashima’s classification scheme) were significantly lower than the pretreatment score at 12 weeks and 1 year after the first dose (both p < 0.0001). No concerns were identified in the efficacy and safety of nalfurafine in patients with specific background, ie, the elderly (aged ≥ 65 years), those with renal impairment, and those on long-term treatment (≥ 365 days) compared with patients without corresponding background.

Conclusion

No new safety issues of concern or cases of insufficient efficacy were identified in this Specific Drug Use Survey of the safety and efficacy of nalfurafine for the improvement of pruritus in patients with chronic liver diseases.

Peptide Kappa Opioid Receptor Ligands and Their Potential for Drug Development

Ligands for kappa opioid receptors (KOR) have potential uses as non-addictive analgesics and for the treatment of pruritus, mood disorders, and substance abuse. These areas continue to have major unmet medical needs. Significant advances have been made in recent years in the preclinical development of novel opioid peptides, notably ones with structural features that inherently impart stability to proteases. Following a brief discussion of the potential therapeutic applications of KOR agonists and antagonists, this review focuses on two series of novel opioid peptides, all-D-amino acid tetrapeptides as peripherally selective KOR agonists for the treatment of pain and pruritus without centrally mediated side effects, and macrocyclic tetrapeptides based on CJ-15,208 that can exhibit different opioid profiles with potential applications such as analgesics and treatments for substance abuse.

Preclinical Studies on Nalfurafine (TRK-820), a Clinically Used KOR Agonist

Nalfurafine has been used clinically in Japan for treatment of itch in kidney dialysis patients and in patients with chronic liver diseases. A one-year post-marketing study showed nalfurafine to be safe and efficacious without producing side effects of typical KOR agonists such as anhedonia and psychotomimesis. In this chapter, we summarize in vitro characterization and in vivo preclinical studies on nalfurafine. In vitro, nalfurafine is a highly potent and moderately selective KOR full agonist; however, whether it is a biased KOR agonist is a matter of debate. In animals, nalfurafine produced anti-pruritic effects in a dose range lower than that caused side effects, including conditioned place aversion (CPA), hypolocomotion, motor incoordination, consistent with the human data. In addition, nalfurafine showed antinociceptive effects in several pain models at doses that did not cause the side effects mentioned above. It appears to be effective against inflammatory pain and mechanical pain, but less so against thermal pain, particularly high-intensity thermal pain. U50,488H and nalfurafine differentially modulated several signaling pathways in a brain region-specific manners. Notably, U50,488H, but not nalfurafine, activated the mTOR pathway, which contributed to U50,488H-induced CPA. Because of its lack of side effects associated with typical KOR agonists, nalfurafine has been investigated as a combination therapy with an MOR ligand for pain treatment and for its effects on opioid use disorder and alcohol use disorder, and results indicate potential usefulness for these indications. Thus, although in vitro data regarding uniqueness of nalfurafine in terms of signaling at the KOR are somewhat equivocal, in vivo results support the assertion that nalfurafine is an atypical KOR agonist with a significantly improved side-effect profile relative to typical KOR agonists.

Chronic Intractable Pruritus in Chronic Kidney Disease Patients: Prevalence, Impact, and Management Challenges - A Narrative Review

Chronic kidney disease (CKD) is recognized as a leading public health problem and causes numerous health complications. One of the most common and burdensome dermatological symptoms affecting patients undergoing dialysis is CKD-associated pruritus (CKD-aP). This condition not only has a negative impact on sleep, mood, daily activities, and quality of life but also increases the mortality risk of hemodialyzed patients. Despite that, this condition is greatly underestimated in clinical practice. Due to the complex and still not fully understood etiopathogenesis of CKD-aP, the choice of an effective therapy remains a challenge for clinicians. Most common therapeutic algorithms use topical treatment, phototherapy, and various systemic approaches. This review aimed to summarize most recent theories about the pathogenesis, clinical features, and treatment of CKD-aP.

The Role of Psychiatric, Analgesic, and Antiepileptic Medications in Chronic Pruritus

Chronic pruritus is a complex yet prevalent concern without a gold standard treatment. The mainstay therapy for chronic pruritus includes topical ointments such as corticosteroids, capsaicin, local anesthetics, antihistamines, and immunomodulators. There are many different subtypes of chronic pruritus, and each unique subtype may benefit from specialized treatments. This review article sheds light on the role of psychiatric, analgesic, and antiepileptic medications in chronic pruritus. We believe that further large-scale studies are needed to determine the true effectiveness of these medications in treating chronic pruritus.

Evaluation of the causes affecting the development of pruritus in patients with peritoneal dialysis

BACKGROUND

Several factors play a role in the pathogenesis of pruritus in uremic patients. The pathophysiology is complex and many factors have been identified in these patients. The aim of this study was to investigate the presence, severity, and possible causes of pruritus in patients with peritoneal dialysis (PD) .

METHODS

Eighty patients, who received continuous ambulatory peritoneal dialysis (CAPD) treatment, were included in this study. Biochemical measurements, parathormone, C-reactive protein (CRP), and vitamin B12 levels of all the patients were recorded. Furthermore, substance P (SP) levels were measured by ELISA methods. Patients were examined by a dermatologist and pruritus degrees were queried using the visual analog score (VAS) with skin dryness.

RESULTS

In generalized linear model analysis, total urea clearance and SP independently predicted VAS scores. SP was significantly predictive in ROC analysis in identifying the VAS score in patients with peritoneal dialysis. The sensitivity and specificity of SP were 80% and 67% (cut-off > 364), respectively, with an area under the ROC curve of 0.757 (95% CI 0.650-0.865, p < 0.001). SP also was significantly predictive in ROC analysis in identifying xerosis in PD patients.

CONCLUSION

Pruritus was proportional to the amount of substance P and total urea clearance was another reason affecting pruritus in peritoneal dialysis patients.

Evaluation of Therapies for Peripheral and Neuraxial Opioid-induced Pruritus based on Molecular and Cellular Discoveries

Opioids are a mainstay of treatment for pain worldwide. Pruritus, a common side effect of opioids, is a patient dissatisfier that limits their use in many clinical settings. Both parenteral and neuraxial administration of opioids frequently evoke pruritus. The ability of opioids to suppress pain while causing itch continues to perplex clinicians and researchers alike. Several mechanisms have been proposed to explain how opioids can give rise to pruritus, but specific knowledge gaps perpetuate debate. This review summarizes the clinical burden of opioid-induced pruritus and emphasizes recent discoveries of peripheral and central mechanisms for opioid-induced pruritus, particularly with respect to scientific and conceptual advances in spinal cord circuitry and mast cell biology. The mechanisms and effectiveness of existing medications used for clinical management of pruritus will be evaluated, and we will highlight the emerging preclinical utility of selective κ-opioid receptor agonists, such as nalfurafine, for the management of opioid-induced pruritus.

Use of Butorphanol as Treatment for Cholestatic Itch

BACKGROUND

Pruritus is a debilitating symptom of cholestatic diseases such as primary biliary cholangitis and primary sclerosing cholangitis and often results in major reduction in quality of life for afflicted patients. Classic treatment options for the treatment of cholestatic pruritus include antihistamines, bile acid resins, serotonin reuptake inhibitors, and mu-opioid antagonists. Unfortunately, these drugs are not always successful in treating pruritus of cholestasis and may be associated with adverse effects. Recent advances in our understanding of itch pathophysiology have led to the use of butorphanol, a kappa-opioid agonist and mu-opioid antagonist, for the treatment of various forms of pruritus. Reports of butorphanol to treat cholestatic itch specifically are rare.

AIMS

To better understand the role of butorphanol in the treatment of cholestatic pruritus, including characterization of its side effect profile.

METHODS

We present a case series of eight adult patients with cholestatic disease who were treated with butorphanol in hopes of alleviating intractable pruritus. Patients were identified through a clinical data request form serviced by University of Miami Information Technology.

RESULTS

Five out of eight patients (62.5%) reported successful reductions in itch severity after treatment with butorphanol, two patients reported no (or transient) change in itch severity, and one patient reported a paradoxical increase in itching. Side effects included somnolence, sedation, nausea, vomiting, and dizziness.

CONCLUSIONS

Butorphanol was safe and leads to clinically significant symptomatic improvement. Clinicians should be aware of butorphanol as an off-label treatment option for pruritus of cholestasis. Further studies are needed to better characterize the effect of butorphanol on cholestatic itch.

Cholestasis-Associated Pruritus and Its Pruritogens

Pruritus is a debilitating symptom of various cholestatic disorders, including primary biliary cholangitis (PBC), primary sclerosing cholangitis (PSC) and inherited progressive familial intrahepatic cholestasis (PFIC). The molecular mechanisms leading to cholestasis-associated pruritus are still unresolved and the involved pruritogens are indecisive. As a consequence of pruritus, patients suffer from sleep deprivation, loss of daytime concentration, auto-mutilation and sometimes even suicidal ideations. Current guideline-approved therapy of cholestasis-associated pruritus includes stepwise administration of several medications, which may alleviate complaints in some, but not all affected patients. Therefore, also experimental therapeutic approaches are required to improve patients' quality of life. This article reviews the current state of research on pruritogens and their receptors, and shortly discusses the most recent experimental therapies.

Central opioid receptors mediate morphine-induced itch and chronic itch via disinhibition

Opioids such as morphine are mainstay treatments for clinical pain conditions. Itch is a common side effect of opioids, particularly as a result of epidural or intrathecal administration. Recent progress has advanced our understanding of itch circuits in the spinal cord. However, the mechanisms underlying opioid-induced itch are not fully understood, although an interaction between µ-opioid receptor (MOR) and gastrin-releasing peptide receptor (GRPR) in spinal GRPR-expressing neurons has been implicated. In this study we investigated the cellular mechanisms of intrathecal opioid-induced itch by conditional deletion of MOR-encoding Oprm1 in distinct populations of interneurons and sensory neurons. We found that intrathecal injection of the MOR agonists morphine or DAMGO elicited dose-dependent scratching as well as licking and biting, but this pruritus was totally abolished in mice with a specific Oprm1 deletion in Vgat+ neurons [Oprm1-Vgat (Slc32a1)]. Loss of MOR in somatostatin+ interneurons and TRPV1+ sensory neurons did not affect morphine-induced itch but impaired morphine-induced antinociception. In situ hybridization revealed Oprm1 expression in 30% of inhibitory and 20% of excitatory interneurons in the spinal dorsal horn. Whole-cell recordings from spinal cord slices showed that DAMGO induced outward currents in 9 of 19 Vgat+ interneurons examined. Morphine also inhibited action potentials in Vgat+ interneurons. Furthermore, morphine suppressed evoked inhibitory postsynaptic currents in postsynaptic Vgat- excitatory neurons, suggesting a mechanism of disinhibition by MOR agonists. Notably, morphine-elicited itch was suppressed by intrathecal administration of NPY and abolished by spinal ablation of GRPR+ neurons with intrathecal injection of bombesin-saporin, whereas intrathecal GRP-induced itch response remained intact in mice lacking Oprm1-Vgat. Intrathecal bombesin-saporin treatment reduced the number of GRPR+ neurons by 97% in the lumber spinal cord and 91% in the cervical spinal cord, without changing the number of Oprm1+ neurons. Additionally, chronic itch from DNFB-induced allergic contact dermatitis was decreased by Oprm1-Vgat deletion. Finally, naloxone, but not peripherally restricted naloxone methiodide, inhibited chronic itch in the DNFB model and the CTCL model, indicating a contribution of central MOR signalling to chronic itch. Our findings demonstrate that intrathecal morphine elicits itch via acting on MOR on spinal inhibitory interneurons, leading to disinhibition of the spinal itch circuit. Our data also provide mechanistic insights into the current treatment of chronic itch with opioid receptor antagonist such as naloxone.

Comparison of Pharmacological Properties between the Kappa Opioid Receptor Agonist Nalfurafine and 42B, Its 3-Dehydroxy Analogue: Disconnect between in Vitro Agonist Bias and in Vivo Pharmacological Effects

Nalfurafine, a moderately selective kappa opioid receptor (KOR) agonist, is used in Japan for treatment of itch without causing dysphoria or psychotomimesis. Here we characterized the pharmacology of compound 42B, a 3-dehydroxy analogue of nalfurafine and compared with that of nalfurafine. Nalfurafine and 42B acted as full KOR agonists and partial μ opioid receptor (MOR) agonists, but 42B showed much lower potency for both receptors and lower KOR/MOR selectivity, different from previous reports. Molecular modeling revealed that water-mediated hydrogen-bond formation between 3-OH of nalfurafine and KOR accounted for its higher KOR potency than 42B. The higher potency of both at KOR over MOR may be due to hydrogen-bond formation between nonconserved Y^7.35 of KOR and their carbonyl groups. Both showed modest G protein signaling biases. In mice, like nalfurafine, 42B produced antinociceptive and antiscratch effects and did not cause conditioned place aversion (CPA) in the effective dose ranges. Unlike nalfurafine, 42B caused motor incoordination and hypolocomotion. As both agonists showed G protein biases, yet produced different effects on locomotor activity and motor incoordination, the findings and those in the literature suggest caution in correlating in vitro biochemical data with in vivo behavior effects. The factors contributing to the disconnect, including pharmacodynamic and pharmacokinetic issues, are discussed. In addition, our results suggest that among the KOR-induced adverse behaviors, CPA can be separated from motor incoordination and hypolocomotion.

Evaluation of Efficacy of Mirtazapine on Pruritus and Serum Histamine and Serotonin Levels in Patients Undergoing Hemodialysis: A Before-After Pilot Clinical Trial

Background

Although chronic kidney disease-associated pruritus (CKD-aP) remains a frequent and frustrating symptom in patients with advanced kidney diseases, its optimal treatments are not well defined. Based on its mechanism of action, as a histamine-1 (H1), 5-(hydroxytryptamine) HT2, and 5HT3-receptor blocker, mirtazapine may be effective in the treatment of CKD-aP. Hence, this study aimed to investigate the efficacy of mirtazapine for the treatment of pruritus in patients undergoing hemodialysis (HD).

Methods

A before-after clinical trial was conducted from September 2018 until March 2019, on 30 HD-patients that had been referred to the HD ward of a tertiary hospital, in Hamadan, Iran. After the 2-week washout period, mirtazapine was administered with a dosage of 15 mg/day for an additional 2 weeks. At baseline and at each dialysis session, the effects of the mirtazapine on the pruritus severity based on the visual analogue scale (VAS) and degree of sleep interference resulting from the pruritus were asked and recorded. Additionally, at the baseline and the end of 2 weeks of treatment, the serum histamine and serotonin levels, as the main chemical pruritogens evoking pruritus symptoms, were also determined.

Results

Twenty-seven patients completed the entire course of the study. Based on the general linear model analysis, a progressive decline in the mean VAS score was observed over time during the study. The mean VAS score decreased from 8.48 ± 1.01 at baseline to 1.04 ±0.79 at the end of treatment (P-value<0.001). Similarly, the mean sleep interference scores were also significantly improved throughout treatment (decreased from 8.07±1.43 to 2.81± 0.74; P-value<0.001). Further, at the end of the treatment, a noticeable decrement in the serum histamine level was also seen (P-value = 0.006). The drug was acceptably well-tolerated and a majority of the patients were satisfied with this treatment.

Conclusion

This pilot study suggests that mirtazapine may be an effective treatment option for the management of CKD-aP. However, further studies would be needed to confirm these results.

Clinical Profiles of Nalfurafine Hydrochloride for the Treatment of Pruritus Patients

Nalfurafine hydrochloride is a selective kappa-opioid agonist that has antipruritic effects. Here we describe the clinical trials for treatment of uremic pruritus in dialysis patients and on hepatic pruritus in patients with chronic liver disease. Among cytochrome P-450 (CYP) isoforms in humans, CYP3A4 is the major isoform involved in metabolic decyclopropylmethylation of nalfurafine hydrochloride. Nalfurafine hydrochloride was found to be a substrate for P-glycoprotein (P-gp), but had no inhibitory effects on P-gp-mediated transport. The efficacy of oral nalfurafine hydrochloride at 2.5 and 5 μg for refractory pruritus in hemodialysis patients was observed within the first 7 days of treatment, and the effects persisted for the 52-week treatment period. Nalfurafine hydrochloride is also effective in the treatment of conventional refractory pruritus in peritoneal dialysis patients. Moreover, nalfurafine hydrochloride at 2.5 and 5 μg is effective for the treatment of refractory pruritus in chronic liver disease patients within the first 7 days of drug administration. In all the clinical trials, most adverse drug reactions (ADRs) were mild and resolved quickly and there was no clinical safety problem. Following 52 weeks of treatment, hemodialysis patients did not develop physical or psychological dependence, indicating no addiction risks. In summary, nalfurafine hydrochloride administered orally at doses of 2.5 and 5 μg was safe and effective for treatment of refractory pruritus in patients undergoing hemodialysis or peritoneal dialysis and in chronic liver disease patients.

Pruritus in patients with chronic liver disease and serum autotaxin levels in patients with primary biliary cholangitis

Background

Pruritus is a common symptom seen in patients with chronic liver disease. However, frequency and severity of pruritus in patients with chronic liver disease is unclear. We investigated frequency, severity and predictive factors of pruritus in these patients from a large cohort.

Methods

A total of 2477 patients with chronic liver disease without allergies or skin diseases were investigated for itch frequency and severity. Itch severity was self-assessed using pruritus scores using the numerical rating scale (NRS). Multivariate regression analysis was performed to identify factors associated with pruritus. Serum autotaxin levels were measured in patients with primary biliary cholangitis (PBC), and the relationship to liver fibrosis and pruritus was analyzed.

Results

The frequency of pruritus in patients with chronic liver disease was significantly higher than in subjects without liver disease (29.8 and 16.2%, respectively, P < 0.001). NRS was high in patients with chronic liver disease, especially in those with PBC, as is generally expected. Multivariate analysis identified lower albumin, higher eosinophil count, and etiology of PBC as independent factors associated with severe pruritus (≥5 points of NRS). In patients with PBC, serum autotaxin levels were significantly correlated with liver fibrosis markers such as platelet count and liver stiffness, and hepatobiliary enzymes such as total bilirubin, aspartate aminotransferase and alkaline phosphatase. However, no significant correlations between serum autotaxin levels and frequency and severity of pruritus were observed in patients with PBC.

Conclusion

The frequency of pruritus was high in patients with chronic liver disease. Reduction of liver function is associated with severe pruritus based on the large number of patients with chronic liver disease. Serum autotaxin is useful for assessing liver fibrosis and severity of cholangitis; however, it is not a predictive marker for severe pruritus in patients with PBC.

Phosphoproteomic approach for agonist-specific signaling in mouse brains: mTOR pathway is involved in κ opioid aversion

Kappa opioid receptor (KOR) agonists produce analgesic and anti-pruritic effects, but their clinical application was limited by dysphoria and hallucinations. Nalfurafine, a clinically used KOR agonist, does not cause dysphoria or hallucinations at therapeutic doses in humans. We found that in CD-1 mice nalfurafine produced analgesic and anti-scratch effects dose-dependently, like the prototypic KOR agonist U50,488H. In contrast, unlike U50,488H, nalfurafine caused no aversion, anhedonia, or sedation or and a low level of motor incoordination at the effective analgesia and anti-scratch doses. Thus, we established a mouse model that recapitulated important aspects of the clinical observations. We then employed a phosphoproteomics approach to investigate mechanisms underlying differential KOR-mediated effects. A large-scale mass spectrometry (MS)-based analysis on brains revealed that nalfurafine perturbed phosphoproteomes differently from U50,488H in a brain-region specific manner after 30-min treatment. In particular, U50,488H and nalfurafine imparted phosphorylation changes to proteins found in different cellular components or signaling pathways in different brain regions. Notably, we observed that U50,488H, but not nalfurafine, activated the mammalian target of rapamycin (mTOR) pathway in the striatum and cortex. Inhibition of the mTOR pathway by rapamycin abolished U50,488H-induced aversion, without affecting analgesic, anti-scratch, and sedative effects and motor incoordination. The results indicate that the mTOR pathway is involved in KOR agonist-induced aversion. This is the first demonstration that phosphoproteomics can be applied to agonist-specific signaling of G protein-coupled receptors (GPCRs) in mouse brains to unravel pharmacologically important pathways. Furthermore, this is one of the first two reports that the mTOR pathway mediates aversion caused by KOR activation.

Recommendations for the Care of Patients Receiving Conservative Kidney Management: Focus on Management of CKD and Symptoms

Conservative kidney management is increasingly accepted as an appropriate treatment option for patients with eGFR category 5 CKD who are unlikely to benefit from dialysis and/or who choose a nondialysis care option. However, there remains great variation in the delivery of their care. As part of the development of a conservative kidney management pathway that is undergoing evaluation, a set of recommendations specific to conservative kidney management for managing the complications of CKD and common symptoms was developed. These recommendations focus on the patient's values and preferences and aim to optimize comfort and quality of life. Explanations for the interventions are provided to support the shared decision-making process between health care professionals, patients, and family members. The recommendations generally emphasize the preservation of function (cognitive, physical, and kidney) and address symptom burden, acknowledging that management priorities can change over time. The recommendations should be used in conjunction with other key elements of conservative kidney management, including clear communication and shared decision making for choosing conservative kidney management, advance care planning, and psychosocial support. Although there are limitations to the existing evidence specific to conservative kidney management, these recommendations are intended as a starting point toward reaching consensus and generating further evidence.

Personalized Approach and Precision Medicine in Supportive and End-of-Life Care for Patients With Advanced and End-Stage Kidney Disease

Kidney supportive care requires a highly personalized approach to care. Precision medicine holds promise for a deeper understanding of the pathophysiology of symptoms and related syndromes and more precise individualization of prognosis and treatment estimates, therefore providing valuable opportunities for greater personalization of supportive care. However, the major drivers of quality of life are psychosocial, economic, lifestyle, and preference-based, and consideration of these factors and skilled communication are integral to the provision of excellent and personalized kidney supportive care. This article discusses the concepts of personalized and precision medicine in the context of kidney supportive care and highlights some opportunities and limitations within these fields.

Role of narrow band ultra violet radiation as an add-on therapy in peritoneal dialysis patients with refractory uremic pruritus

AIM

To assess the role of narrow band ultraviolet B (UVB) as a treatment option in peritoneal dialysis patients with refractory uremic pruritus.

METHODS

In this retrospective study, 29 adult patients with end stage renal failure on peritoneal dialysis, and who had refractory uremic pruritus, were given narrow band UVB radiation as an add-on therapy to standard care for a duration of 12 wk. The response to the pruritus was assessed both weekly and at the end of the study period using a visual analogue score (VAS).

RESULTS

The average VAS score at the end of the study was 3.14 ± 1.59, which was significant compared to the baseline value of 7.75 ± 1.02 (P < 0.05). Improvements in symptoms were noted in 19 out of 21 (90.4%) patients. However, relapse occurred in six out of the 19 patients who responded. The dropout rate was high during the study period (33.3%).

CONCLUSION

Narrow band UVB is effective as an add-on therapy in peritoneal dialysis patients with refractory uremic pruritus. However, the present regime is cumbersome and patient compliance is poor.

Pruritus: Progress toward Pathogenesis and Treatment

Pruritus, the most common cutaneous symptom, is widely seen in many skin complaints. It is an uncomfortable feeling on the skin and sometimes impairs patients' quality of life. At present, the specific mechanism of pruritus still remains unclear. Antihistamines, which are usually used to relieve pruritus, ineffectively work in some patients with itching. Recent evidence has suggested that, apart from histamine, many mediators and signaling pathways are involved in the pathogenesis of pruritus. Various therapeutic options for itching correspondingly have been developed. In this review, we summarize the updated pathogenesis and therapeutic strategies for pruritus.

Post-marketing surveillance study of the safety and efficacy of nalfurafine hydrochloride (Remitch® capsules 2.5 μg) in 3,762 hemodialysis patients with intractable pruritus

Background

Intractable pruritus in hemodialysis patients can significantly decrease their quality of life and is also associated with poor vital prognosis. Although combined multiple causes of intractable pruritus in these patients have been identified, no existing treatments are proven to be sufficiently effective. We conducted a post-marketing surveillance to follow-up and assess the safety and efficacy of nalfurafine, a selective κ-opioid receptor agonist, for the treatment of intractable pruritus in patients undergoing hemodialysis.

Patients and methods

Hemodialysis patients with intractable pruritus from institutions in Japan who received oral nalfurafine hydrochloride between January 2010 and December 2013 were enrolled in the surveillance. Surveillance was completed in July 2015. Safety data during 1 year after nalfurafine treatment onset, and efficacy data of nalfurafine evaluating the first 12-week treatment period and the following period until 1 year after the initial dose of nalfurafine (using global assessment of the itch improvement by the physician, Visual Analog Scale, and the Shiratori's severity scores) were collected and analyzed.

Results

In total, 3,762 patients were analyzed for safety. Adverse drug reactions were experienced by 402/3,762 (10.69%) patients. The most frequent adverse drug reactions were insomnia (127/3,762 [3.38%] patients), constipation (34 [0.90%]), somnolence (32 [0.85%]), dizziness (23 [0.61%]), nausea (13 [0.35%]), and malaise (9 [0.24%]). No patients developed dependence on nalfurafine. Nalfurafine was effective in 82.50% (2,880/3,491) of patients during the first 12 weeks and in 84.95% (2,167/2,551) on treatment during the subsequent period until 1 year after nalfurafine treatment initiation. Statistically significant decreases were reported in the Visual Analog Scale and the Shiratori's severity scores (p<0.001).

Conclusion

Oral nalfurafine hydrochloride (from 2.5 μg/day to a maximum of 5.0 μg/day) continues to be safe and effective for the treatment of intractable pruritus in hemodialysis patients in real-world clinical settings.

Predictors of pruritus in patients with chronic liver disease and usefulness of nalfurafine hydrochloride

AIM

Pruritus is one of the complications of chronic liver disease, and it is important to investigate the predictors.

METHODS

Six hundred and seventy-three consecutive Japanese patients with chronic liver disease were retrospectively investigated for itch severity. Furthermore, 138 of all 673 patients were introduced to nalfurafine hydrochloride, and the improvement of itch severity was evaluated. The itch severity was self-assessed using the pruritus scores by Kawashima's criteria and visual analog scale.

RESULTS

Two hundred and twenty-nine of the 673 patients (34.0%) were evaluated as 1 point or more of pruritus severity of Kawashima's criteria, and 46 patients (6.8 %) as 3 points or more. Multivariate analysis established that being negative for hepatitis B surface antigen (HBsAg) and presence of hepatocellular carcinoma (HCC) were significant determinants of pruritus (≥1 point of Kawashima's criteria), and being negative for HBsAg and having lower levels of platelet count were significant determinants of severe pruritus (≥3 points). Ninety-three of the 138 patients (67.4%) with nalfurafine hydrochloride indicated improvement of itch, defined as a decrease in VAS of 50 mm or more. There were no significant differences in treatment efficacy of nalfurafine hydrochloride, regardless of the three predictors of pruritus (HBsAg, HCC and platelet count).

CONCLUSION

The present retrospective study indicated the predictors for pruritus, based on the large number of patients with chronic liver disease. Furthermore, this study demonstrated that nalfurafine hydrochloride may be useful for pruritus, regardless of the predictors.

Efficacy of nalfurafine hydrochloride in patients with chronic liver disease with refractory pruritus: A randomized, double-blind trial

AIMS

Patients with chronic liver disease sometimes develop cholestasis, which induces severe whole-body pruritus that may disrupt daily activities and sleep. To determine the efficacy of nalfurafine hydrochloride (5 μg), which is a selective κ-opioid receptor agonist, in improving pruritus, we undertook a double-blind placebo-controlled study in patients with chronic liver disease with refractory pruritus. Nalfurafine hydrochloride at 2.5 μg was also used to evaluate the dose-response relationship.

METHODS

In total, 318 subjects were randomly assigned to receive the placebo or nalfurafine hydrochloride (2.5 or 5 μg) given orally once daily for 84 consecutive days. Pruritus was assessed based on the visual analog scale and pruritus scores.

RESULTS

Changes in the visual analog scale at week 4 (last observation carried forward) were significantly greater in the nalfurafine hydrochloride groups at 28.56 and 27.46 mm in the 2.5 μg and 5 μg groups, respectively, compared to 19.25 mm in the placebo group (P = 0.0022 and 0.0056, respectively). The major adverse drug reactions (ADRs) included pollakiuria (including nocturia), somnolence, insomnia (including middle insomnia), and constipation. Most ADRs were mild.

CONCLUSIONS

Nalfurafine hydrochloride (2.5 or 5 μg daily) was effective in the treatment of refractory pruritus in patients with chronic liver disease. Furthermore, no clinically significant ADRs were observed at either dose.

Blood lead level is a positive predictor of uremic pruritus in patients undergoing hemodialysis

Although uremic pruritus (UP) is a common and annoying symptom for end-stage renal disease patients on hemodialysis (HD) and peritoneal dialysis, its pathogenesis is poorly understood. However, systemic inflammation is one of the possible pathogenesis of UP, and blood lead level (BLL) has been noted to be associated with inflammation and nutritional status in long-term HD patients. There might be an interaction or association, therefore, between BLL and UP through systemic inflammation. We analyzed cross-sectional data among 866 participants. All of the 866 patients in this study were stratified into groups with low-normal (<10 μg/dL), high-normal (10-20 μg/dL), and abnormal BLLs (>20 μg/dL). The associations between UP and BLL and the clinical data were analyzed. Multivariate logistic regression demonstrated that HD duration, non-anuria, log ferritin, serum low-density lipoprotein, log BLL, high-normal BLL, and high BLL were associated with UP. In conclusion, BLL was positively associated with UP.

Long-term efficacy and safety of nalfurafine hydrochloride on pruritus in chronic liver disease patients: Patient-reported outcome based analyses

Background and aim

Among various symptoms accompanied with chronic liver disease, pruritus affects the quality of life of patients, causing physical and mental stress, and worsens hepatic function. Recently, κ-opioid receptor agonist, nalfurafine hydrochloride was approved to treat central pruritus in patients with liver disease in Japan. This study aimed to assess the long-term efficacy and safety of nalfurafine hydrochloride on pruritus in chronic liver disease patients.

Methods

A patient-reported outcome using questionnaire-based methods was used for 41 liver disease patients with or without pruritus symptoms. Nalfurafine hydrochloride (2.5 μg/day) was orally administered to 18 patients suffering from pruritus symptoms and whose current treatment was not effective. The same questionnaires and visual analogue scales (VAS) were repeatedly followed up for the patients for the entire follow-up period, and biochemical analyses were performed to evaluate the safety of the treatment.

Results

Pruritus completely disappeared in seven of 18 cases, and VAS scores showed a decreasing trend over time from the start of nalfurafine hydrochloride administration in all patients who received the medication. Among 11 patients who were followed up for more than 12 weeks, nine patients showed continuous improvement of symptoms, and this progress was still apparent at ≥20 weeks after starting administration (p < 0.0001). The medication was discontinued in four patients because of progression of primary disease, high cost, oral dryness, and anemia. No significant toxicity was observed on the serum biochemical analyses.

Conclusions

Nalfurafine hydrochloride contributed to long-term suppression of pruritus without significant safety problems.

Adjunctive Management of Itch in Atopic Dermatitis

Itch, or pruritus, is a hallmark feature of atopic dermatitis (AD). The impact of AD-related pruritus can range from mildly distressing or distracting to completely disabling. Traditionally, management of itch in AD patients has focused on restoring the altered skin barrier with topical emollients and/or reducing inflammation. A growing emphasis has been placed on directly targeting the neural transmission pathways that mediate itch signaling. Off-label use of neuromodulatory agents has helped reduce this aggravating symptom in atopic patients. This article reviews the current literature on the use of neuromodulatory agents and nonpharmacologic alternative therapies used to treat AD-related pruritus.

Sleep Related Scratching: A Distinct Parasomnia?

ABSTRACT

Pruritus (itching) during the sleep period can present as a symptom of dermatological or systemic disease, or as a parasomnia. Sleep related scratching as a primary parasomnia, exclusively confined to sleep in the absence of coexisting dermatological disorders, has not been well described. This case series describes three such patients, and discusses potentially relevant pathophysiology that can underlie itching or pain. Such cases of sleep related scratching may merit nosologic classification apart from previously defined parasomnias.

Targeting the Opioid Pathway for Uremic Pruritus: A Systematic Review and Meta-analysis

BACKGROUND

Patients undergoing hemodialysis or peritoneal dialysis often experience pruritus which is associated with morbidity and mortality. One proposed treatment approach is to target the opioid pathway using either µ-opioid antagonists or κ-opioid agonists.

OBJECTIVE

To review the efficacy of targeting the opioid pathway for pruritus among dialysis patients (uremic pruritus).

DESIGN

Systematic review and meta-analysis.

SETTING/METHODS

The systematic review included randomized controlled and randomized crossover trials identified in the MEDLINE, EMBASE, and Cochrane databases (1990 to June 2014) evaluating the efficacy of µ-opioid antagonists or κ-opioid agonists in the treatment of uremic pruritus.

PATIENTS

Adult (≥18 years) chronic dialysis patients.

MEASUREMENTS

The primary outcome being evaluated was reduction in itch severity measured on a patient-reported visual analog scale (VAS).

RESULTS

Five studies out of 3587 screened articles met the inclusion criteria. Three studies evaluated the efficacy of naltrexone, a µ-opioid antagonist, and 2 studies evaluated the efficacy of nalfurafine, a κ-opioid agonist. Duration of included studies was short, ranging from 2 to 9 weeks.

LIMITATIONS

Due to the heterogeneity in reporting of outcomes, data from the studies evaluating naltrexone could not be pooled. Pooled analysis, using a random effects model, found that use of nalfurafine resulted in a 9.50 mm (95% confidence interval [CI], 6.27-12.74, P < .001) greater reduction of itch severity (measured on a 100-mm VAS) than placebo in the treatment of uremic pruritus.

CONCLUSIONS

Nalfurafine holds some promise with respect to the treatment of uremic pruritus among dialysis patients. However, more long-term randomized controlled trials evaluating the efficacy of therapies targeting the opioid pathway for uremic pruritus are required.

Effects of Intrathecal κ-Opioid Receptor Agonist on Morphine-Induced Itch and Antinociception in Mice

The μ-opioid receptor (MOR) agonist-induced itch is a significant issue associated with analgesic therapies. Research suggested that systemically administered κ-opioid receptor (KOR) agonists inhibit intrathecal morphine-induced itch in primates. However, serious adverse effects induced by systemically administered KOR agonists may restrict their usefulness in humans. We investigated the effects of intrathecal KOR agonists on intrathecal morphine-mediated itch and antinociception in mice.Mice received intrathecal injections of one of the following drugs: morphine (0.1-1.0 nmol), the selective KOR agonist TRK-820 100 pmol, the combination of morphine 0.3 nmol + TRK-820 (10-100 pmol), and 5 μL of saline. One hour after intraperitoneal administration of the selective KOR antagonist nor-binaltorphimine 1.0 μmol, the effect of TRK-820 100 pmol on intrathecal morphine 0.3 nmol-induced scratching was tested. Total numbers of scratches after intrathecal injection were analyzed. After observing scratching behavior, sedation level was evaluated subjectively. Nociceptive threshold was determined by tail immersion test with intrathecal injections of the following agents: morphine (0.1-1.0 nmol), TRK-820 (10-100 pmol), morphine 0.1 nmol + TRK-820 10 pmol, and 5 μL of saline.Intrathecal TRK-820 dose-dependently inhibited intrathecal morphine-induced scratching compared with that in the saline group. Intraperitoneal nor-binaltorphimine completely inhibited the antiscratching effect of intrathecal TRK-820 100 pmol. The combination of morphine 0.3 nmol and TRK-820 did not alter the sedation score compared with that in the morphine 0.3 nmol group. Morphine 0.1 nmol + TRK-820 10 pmol significantly produced greater thermal antinociceptive effects than morphine 0.1 nmol.We demonstrated that intrathecal KOR agonists exert antipruritic effects on intrathecal morphine-induced itch without affecting sedation. The combination of intrathecal morphine and intrathecal KOR agonists produces more potent antinociceptive effects against a thermal stimulus compared with morphine alone.

[Treatment of chronic itch in systemic disease. Current standards]

Chronic itch (CI) is a frequent and sometimes tormenting symptom in many skin and systemic diseases. In systemic diseases, it mostly appears on primarily unaffected skin. As a sequelae of intense scratching, secondary skin lesions such as excoriations, scars, and prurigo nodularis may occur. Due to the lack of valid pathogenetic concepts and good clinical trials, the therapy of CI remains mostly symptomatic. In Europe almost all drugs used to treat CI are not approved for this indication. CI is frequent in patients with chronic kidney diseases in advanced stages. Gabapentin and pregabalin, anticonvulsants, and centrally acting calcium channel blockers have been shown to exert a profound effect in CI. Furthermore, UVB phototherapy has been proven to attenuate pruritus in uremic patients. Randomized controlled studies have recently shown that nalfurafine, a κ-opioid receptor agonist, is able to ameliorate itch in patients with uremic itch. In patients suffering from cholestatic itch, the anion exchange resin colestyramine and rifampicin are effective antipruritic drugs. Furthermore, µ-opioid receptor antagonists and sertraline may be used to alleviate CI in hepatic diseases. In refractory cases, naso-biliary drainage or albumin dialysis are effective invasive procedures. For the treatment of chronic itch in hematological diseases no controlled trials have been performed so far. The mainstay in these cases is to treat the underlying disease.

Methods for preclinical assessment of antipruritic agents and itch mechanisms independent of mast-cell histamine

Itch is a sensation that provokes a desire to scratch. Mast-cell histamine was thought to be a key itch mediator. However, histamine and mast-cell degranulation were reported not to elicit scratching in animals. It was difficult to investigate the pathophysiology of itching and to evaluate the antipruritic efficacy of chemical agents in the early 1990 s. We showed that hind-paw scratching and biting were elicited by stimulation with pruritogenic agents in mice. Those results demonstrated for the first time that cutaneous itching could be evaluated behaviorally in animals. We established various animal models of pathological itch of the skin (dry skin, mosquito allergy, surfactant-induced pruritus, and herpes zoster) and mucus membranes (pollen allergy). Mast-cell histamine did not play a key role in itching in any animal model examined except for the pollen allergy model. Histamine is not an exclusive itch mediator of mast cells; tryptase and leukotriene B4 released from mast cells also act as itch mediators. Epidermal keratinocytes release several itch mediators, such as leukotriene B4, sphingosylphosphorylcholine, thromboxane A2, nociceptin, nitric oxide, and histamine, which may play important roles in pathological itching. Appropriate animal models of pathological itching are needed for pharmacological evaluation of the antipruritic efficacy of chemical agents.

Investigation of the role of βarrestin2 in kappa opioid receptor modulation in a mouse model of pruritus

The kappa opioid receptor (KOR) is involved in mediating pruritus; agonists targeting this receptor have been used to treat chronic intractable itch. Conversely, antagonists induce an itch response at the site of injection. As a G protein-coupled receptor (GPCR), the KOR has potential for signaling via G proteins and βarrestins, however, it is not clear which of these pathways are involved in the KOR modulation of itch. In this study asked whether the actions of KOR in pruritus involve βarrestins by using βarrestin2 knockout (βarr2-KO) mice as well as a recently described biased KOR agonist that biases receptor signaling toward G protein pathways over βarrestin2 recruitment. We find that the KOR antagonists nor-binaltorphimine (NorBNI) and 5'-guanidinonaltrindole (5'GNTI) induce acute pruritus in C57BL/6J mice, with reduced effects in KOR-KO mice. βArr2-KO mice display less of a response to KOR antagonist-induced itch compared to wild types, however no genotype differences are observed from chloroquine phosphate (CP)-induced itch, suggesting that the antagonists may utilize a KOR-βarrestin2 dependent mechanism. The KOR agonist U50,488H was equally effective in both WT and βarr2-KO mice in suppressing CP-induced itch. Furthermore, the G protein biased agonist, Isoquinolinone 2.1 was as effective as U50,488H in suppressing the itch response induced by KOR antagonist NorBNI or CP in C57BL/6J mice. Together these data suggest that the antipruritic effects of KOR agonists may not require βarrestins.

Salvinorin A analogues PR-37 and PR-38 attenuate compound 48/80-induced itch responses in mice

BACKGROUND AND PURPOSE

The opioid system plays a crucial role in several physiological processes in the CNS and in the periphery. It has also been shown that selective opioid receptor agonists exert potent inhibitory action on pruritus and pain. In this study we examined whether two analogues of Salvinorin A, PR-37 and PR-38, exhibit antipruritic properties in mice.

EXPERIMENTAL APPROACH

To examine the antiscratch effect of PR-37 and PR-38 we used a mouse model of compound 48/80-induced pruritus. In order to elucidate the mechanism of action of tested compounds, specific antagonists of opioid and cannabinoid receptors were used. The effect of PR-37 on the CNS was assessed by measuring motor parameters and exploratory behaviours in mice.

KEY RESULTS

PR-37 and PR-38, jnjected s.c., significantly reduced the number of compound 48/80-induced scratching behaviours in mice in a dose- and time-dependent manner. PR-38 was also active when orally administered. The antiscratch activity of PR-37 was blocked by the selective κ opioid receptor antagonist, nor-binaltorphimine, and that of PR-38 by the selective μ opioid receptor antagonist, β-funaltrexamine.

CONCLUSION AND IMPLICATIONS

In conclusion, a novel framework for the development of new antipruritic drugs derived from salvinorin A has been validated.

Pruritus in Systemic Diseases: A Review of Etiological Factors and New Treatment Modalities

Pruritus is the most frequently described symptom in dermatology and can significantly impair the patient's quality of life. In 10–50% of adults with persistent pruritus, it can be an important dermatologic clue for the presence of a significant underlying systemic disease such as renal insufficiency, cholestasis, hematologic disorder, or malignancy (Etter and Myers, 2002; Zirwas and Seraly, 2001). This review describes the presence of pruritus in different systemic diseases. It is quite important to discover the cause of pruritus for providing relief for the patients experiencing substantial morbidity caused by this condition.

Nalfurafine hydrochloride to treat pruritus: a review

Uremic pruritus has a great negative influence on quality of life in hemodialysis (HD) patients and, importantly, negatively affects mortality risk. Recently, nalfurafine hydrochloride, an opioid κ-selective agonist, has been officially approved for resistant pruritus in HD patients on the basis of a well-evidenced clinical trial in Japan. From clinical observation, it has been suggested that the upper neuron system plays a role in its pathogenesis. According to previous experimental results, using mice injected with opioids, dynorphin suppresses itch through binding κ-opioid receptors, suggesting that κ-opioid opioid receptor agonists act as potential therapeutic reagents for pruritus in HD patients. In Japan, a large-scale placebo-controlled study was performed to examine the efficacy and safety of oral nalfurafine hydrochloride for intractable pruritus in 337 HD patients. Two daily doses of 2.5 or 5 μg nalfurafine or placebo were orally administered for 2 weeks, and clinical responses were analyzed. The results showed that the mean decrease in the visual analog scale for pruritus from baseline was 22 mm in the 5 μg nalfurafine hydrochloride group (n=114) and 23 mm in the 2.5 μg group (n=112). These reductions were statistically significant compared with 13 mm, which is the mean decrease of visual analog scale in the placebo group (n=111), demonstrating that nalfurafine is an effective and safe drug for uremic pruritus in HD patients. Moreover, another open-label trial (n=145) examining the long-term effect of 5 μg oral nalfurafine revealed the maintenance of the antipruritic effect of nalfurafine for 52 weeks. In addition, on the basis of recent data showing κ-opioid receptor expression in the epidermis of atopic dermatitis and psoriasis, nalfurafine hydrochloride also can be potentially used for these two skin diseases.

Pharmacokinetics of nalbuphine hydrochloride extended release tablets in hemodialysis patients with exploratory effect on pruritus

BACKGROUND

Uremic pruritus is a common and deleterious condition among hemodialysis (HD) patients. Central gating of μ/κ opiate circuitry plays an important role in mediating and countering pruritogenic sensation. The objective of this study was to assess the safety and pharmacokinetics (PK) of the mixed μ-antagonist/κ-agonist nalbuphine, administered orally as nalbuphine HCl extended release (ER) tablets in HD patients, and explore its effect on pruritus.

METHODS

In this open-label multiple escalating dose study, 15 HD patients with pruritus and 9 matched healthy subjects were enrolled. Nalbuphine HCl ER dose was escalated from 30 mg QD to 240 mg BID over 15 days. A full PK profile was obtained under dialysis and non-dialysis conditions as a function of dose. Clearance during dialysis was determined by sampling dialysate and arterial/venous blood during dialysis. Pruritus severity was assessed twice daily using a Visual Analog Scale (VAS). Safety monitoring included extensive monitoring of EKG, blood pressure, and pulse oximetry.

RESULTS

In HD patients, nalbuphine concentration peaked within 4-9 hours and attained steady state within 2-3 days, with no significant accumulation. Mean half-life was 14.2 hours, mean Cmax and AUCtau ranged between 13 and 83 ng/mL and 118 and 761 ng∙h/mL, respectively, with exposure increasing in a nearly dose-proportional fashion. Exposure in HD patients was about 2-fold higher than in healthy subjects. There was no meaningful difference between exposure on dialysis and non-dialysis days with 1% or less of the dose removed by dialysis. Nalbuphine suppressed itch in a dose-dependent manner, reducing mean VAS score from 4.0 to 1.2 at 180 mg and 0.4 at 240 mg.

CONCLUSIONS

Nalbuphine HCl ER tablets can be safely administered to HD patients without dose adjustment up to 240 mg BID and may hold promise in treating uremic pruritus.

Nalfurafine suppresses pruritogen- and touch-evoked scratching behavior in models of acute and chronic itch in mice

The kappa-opioid agonist, nalfurafine, has been approved in Japan for treatment of itch in patients with chronic kidney disease. We presently investigated if systemic administration of nalfurafine inhibited ongoing or touch-evoked scratching behavior (alloknesis) following acute intradermal injection of histamine or the non-histaminergic itch mediator, chloroquine, in mice. We also investigated if nalfurafine suppressed spontaneous or touch-evoked scratching in an experimental model of chronic dry skin itch. Nalfurafine reduced scratching evoked by histamine and chloroquine. Following acute histamine, but not chloroquine, low-threshold mechanical stimuli reliably elicited directed hindlimb scratching behavior, which was significantly attenuated by nalfurafine. In mice with experimental dry skin, nalfurafine abolished spontaneous scratching but had no effect on alloknesis. Nalfurafine thus appears to be a promising treatment for acute itch as well as ongoing itch of dry skin.

Targeting Itch with Ligands Selective for κ Opioid Receptors

Several chemically diverse pruritogens, including bombesin, compound 48/80, norbinaltorphimine, and 5'-GNTI, cause rodents to scratch excessively in a stable, uniform manner and consequently provide convenient animal models of itch against which potential antipruritics may be evaluated, structure-activity relationships established, and the nature of spontaneous, repetitive behavior itself analyzed. Decreasing the number of scratching bouts in these apparently simple models has been the requisite first step in the progress of kappa opioid agonists such as nalbuphine, asimadoline, and CR845 toward clinical testing as antipruritics. Nalfurafine is the prime example of a kappa agonist spanning the developmental divide between scratching mice models and commercialization within 10 years. Patients undergoing hemodialysis and suffering from the itching associated with uremic pruritus, and potentially those inflicted with atopic dermatitis, are the beneficiaries.