Opioid peptides and primary biliary cirrhosis

Psyche, opioids, and itch: therapeutic consequences

A patient's psychological condition can substantially affect the presence and severity of pruritus, a phenomenon thought to be mediated by the central nervous system's (CNS) opioid neurotransmitter system. Specific psychodermatologic disorders associated with psychogenic pruritus, including depression, anxiety, chronic tactile hallucinations, delusions of parasitosis, neurotic excoriations, and other cutaneous compulsions are likely controlled by this pathway. Therefore, in treating these conditions, medications specifically directed at the CNS can be the most effective therapies, whereas topical and supportive therapy may be important adjuncts in targeting the associated pruritus. Furthermore, the impact of an understanding clinician and a good physician-patient relationship cannot be underestimated in determining ultimate prognosis. This review will begin by discussing the relationship between the psyche and pruritus as well as the opioid neurotransmitter system. Following this, several disorders characterized by psychogenic pruritus will be described, and CNS-specific and adjunctive topical and supportive therapies for these conditions will be detailed.

Contribution of endogenous opioids and nitric oxide to papillary muscle contractile impairment in cholestatic rats

Attenuated responsiveness to adrenoceptor stimulation has been proposed as an important factor underlying cardiovascular complications of cholestasis. We examined isolated papillary muscle responsiveness to alpha (phenylephrine) and beta-adrenoceptor (isoproterenol) agonists in 7-day bile duct-ligated rats. We investigated the role of nitric oxide (NO) and endogenous opioids in papillary muscle hyporesponsiveness to isoproterenol stimulation. In order to evaluate the effect of NO and endogenous opioids, animals were treated with chronic subcutaneous injections of N(omega)-nitro-L-arginine methyl ester (L-NAME, 10 mg/kg/day) or naltrexone (20 mg/kg/day), or isolated papillary muscles were exposed acutely to the same drugs (10(-4) and 10(-6) M, respectively) in an organ bath. The basal contractile force of papillary muscle, +dT/dtmax and -dT/dtmax, was significantly decreased in bile duct-ligated rats compared to sham-operated ones (P<0.05, for each value). The concentration-response curve for phenylephrine and isoproterenol demonstrated a reduced maximum effect in bile duct-ligated rats compared to the sham-operated group (P<0.01 and 0.05, respectively). Basal contractile abnormalities of bile duct-ligated rats were corrected by L-NAME or naltrexone treatment, either acute or chronic. While chronic L-NAME treatment resulted in a left-ward shift (P<0.05), it had no effect on the maximum effect in bile duct-ligated rats. Acute L-NAME treatment did not influence isoproterenol responsiveness. Acute and chronic naltrexone treatment resulted in partial and complete correction of the hyporesponsiveness of bile duct-ligated rats, respectively (P<0.05). This investigation demonstrates that the papillary muscles of 7-day bile duct ligated-rats have an impaired basal contractility and hyporesponsiveness to both alpha and beta-adrenoceptor stimulation. It also provides evidence for the involvement of increased opioidergic tone and NO overproduction in cholestasis-induced cardiac impairment.

Cholestatic liver disease modulates susceptibility to ischemia/reperfusion-induced arrhythmia, but not necrosis and hemodynamic instability: the role of endogenous opioid peptides

BACKGROUND/AIMS

Acute cholestasis is associated with cardiovascular complications, which mainly manifest during stressful conditions. The goal of this study is to evaluate susceptibility of 7-day bile duct-ligated rats to ischemia/reperfusion-induced injury.

METHODS

Sham-operated and cholestatic rats, treated with daily normal saline, L-NAME (a non-selective NO synthase inhibitor) naltrexone, or both L-NAME and naltrexone were subjected to 30 min of ischemia followed by 2 h of reperfusion.

RESULTS

Cholestatic rats demonstrated significant bradycardia, hypotension (P < 0.01), and QT prolongation (P < 0.001). The incidence of premature ventricular contractions (P < 0.01), incidence and duration of ventricular tachycardia (P < 0.05), but not ventricular fibrillation, were significantly lower in cholestatic rats. There was no significant difference in hemodynamic instability and infarct size between the groups. L-NAME corrected QT prolongation in cholestatic rats (P < 0.05), with no effect on heart rate, blood pressure and arrhythmia. Naltrexone restored normal heart rate (P < 0.05), blood pressure (P < 0.05) and susceptibility to arrhythmia (P < 0.05) in cholestatic animals, with no significant effect on QT interval. L-NAME and naltrexone co-administration corrected bradycardia (P < 0.05), hypotension (P < 0.05), QT prolongation (P < 0.05) and abolished resistance of cholestatic rats against arrhythmia (P < 0.05).

CONCLUSIONS

This study suggests that short-term cholestasis is associated with resistance against ischemia/reperfusion-induced arrhythmia, which depends on availability of endogenous opioids.

The delta opioid receptor 1 is expressed by proliferating bile ductules in rats with cholestasis: implications for the study of liver regeneration and malignant transformation of biliary epithelium

In sharp contrast with the normal adult liver, the fetal human and rat livers and the liver of rats with cholestasis secondary to bile duct resection express the preproenkephalin mRNA, which codes for the endogenous opioid peptide Met-enkephalin. Furthermore, Met-enkephalin immunoreactivity is detected in hepatocytes and in proliferating bile ductules in the cholestatic rat liver. These data suggest that in cholestasis endogenous opioids may have a local effect in the cholestatic liver. As endogenous opioids exert their effect by binding to opioid receptors, the presence of opioid receptors in the cholestatic livers would support the hypothesis that Met-enkephalin plays a role in situ. Preliminary data presented in this manuscript reveals the expression of the delta opioid receptor in the liver of rats with cholestasis. This finding suggests that there is a scenario in which Met-enkephalin can bind to opioid receptors in the liver in cholestasis to exert a local effect. In vivo studies in this model of cholestasis with the use of opioid agonist and antagonist will shed light on the possible role of opioidergic regulation of liver regeneration. Studies on the effect of opiate antagonists on the evolution of cholestasis in this animal model may provide insight into the mechanisms of liver regeneration. In addition, as some conditions associated with cholestasis and bile ductular proliferation can be complicated by malignancy, the expression of the delta opioid receptor in malignant tumors of the biliary tree merits research.

Spontaneous scratching behavior in MRL/lpr mice, a possible model for pruritus in autoimmune diseases, and antipruritic activity of a novel κ-opioid receptor agonist nalfurafine hydrochloride

Pruritus is a common, distressing and difficult to manage complication of many autoimmune diseases. A suitable animal model of autoimmune disease associated pruritus would contribute to a better understanding of the pathophysiology of this symptom and lead to the development of safe and effective antipruritic agents. We noticed spontaneous scratching behavior in aged MRL/lpr mice, a model of autoimmune disease. This scratching behavior was observed in a specific pathogen-free environment and was more frequent in female mice. In contrast to animal models of dermatitis; NC/Nga mice, the serum IgE and IgG1 levels in MRL/lpr mice were not elevated. These features indicate that this scratching behavior is similar to human autoimmune disease associated pruritus. The antipruritic effects of an antihistamine (chlorpheniramine), an opioid receptor antagonist (naltrexone), and a novel kappa-opioid receptor agonist (nalfurafine hydrochloride [TRK-820]) were evaluated. The frequency of scratching was not reduced by oral administration of chlorpheniramine, suggesting that the behavior is antihistamine-resistant. The oral administration of nalfurafine and subcutaneously administered naltrexone inhibited the scratching behavior without causing gross behavioral changes. In conclusion, MRL/lpr mice scratching behavior is a suitable model of pruritus that occurs in autoimmune diseases, and nalfurafine was shown to be efficacious against this behavior suggesting that it may be beneficial in patients with autoimmune disease associated pruritus.

A controlled trial of ondansetron in the pruritus of cholestasis

BACKGROUND

In patients with pruritus of cholestasis, response to conventional drug treatment may be unsatisfactory. Activation of 5-hydroxytryptamine receptors on dermal sensory nerve-endings plays a role in the perception of pruritus. The 5-hydroxytryptamine(3) receptor antagonist, ondansetron, has been used in the treatment of pruritus of cholestasis, but there are few controlled data.

AIM

To determine whether ondansetron is effective in treating the pruritus of cholestasis.

METHODS

A total of 19 patients with resistant pruritus were randomized, double blind, to receive either ondansetron 8 mg or placebo as a single intravenous bolus, followed by oral ondansetron 8 mg or placebo twice daily for 5 days. Patients' perception of pruritus was recorded hourly using a visual analogue scale, and scratching activity measured by means of a piezo-electric crystal attached to the fingernail.

RESULTS

Mean pruritus score using visual analogue scale and scratching activity were reduced on the first treatment day compared with baseline in both the ondansetron and placebo groups (P < 0.05), but there were no significant differences in mean pruritus perception or scratching activity between the two groups.

CONCLUSION

Ondansetron was of no benefit in this group of pruritic patients during short-term treatment.

Obstructive cholestasis alters intestinal transit in mice: role of opioid system

Acute cholestasis is associated with increased activity of the endogenous opioid system. It is also known that opioid receptor agonists like morphine decrease the intestinal transit. The purpose of the present study was to investigate the effect of cholestasis on the small intestine transit and the possible involvement of opioid system in this phenomenon in mice. Cholestasis was induced by bile duct-ligation and intestinal transit was measured with charcoal meal and calculation of percent of transit through small intestine. The effect of chronic administration of naltrexone and acute pretreatment with morphine on intestinal transit was evaluated in bile duct-ligated (BDL) as well as unoperated (CTL) and sham-operated (SHAM) animals. The plasma alkaline phosphatase and alanine aminotransferase activities were also measured. A significant decrease in small intestine transit (%transit) was observed in BDL mice compared to SHAM animals, which was prominent even after 24 h of cholestasis. Chronic pretreatment with an opioid receptor antagonist, naltrexone, (10 mg/kg, i.p for 2, 4 or 6 days) completely restored the cholestasis-induced decrease in %transit to that of control animals. Although the acute administration of morphine (2 mg/kg, s.c.) 20 min before charcoal feeding caused a significant decrease in the intestinal transit of CTL and SHAM animals, it did not decrease the %transit of BDL animals on the day 5 after operation. Our findings show that acute cholestasis is associated with a prominent decrease in small intestine transit in mice and opioid receptors maybe involved in this phenomenon.

Treatment of the pruritus of cholestasis

The etiology of the pruritus of cholestasis is unknown. It is inferred that the pruritogen(s) is produced in the liver, excreted in bile, and as a result of cholestasis it accumulates in plasma. It may follow, logically, that the removal of the substance(s) that mediate pruritus leads to its resolution. The problem with this approach, however, is that the substance(s) is unknown; thus, it is not possible to reduce its serum levels specifically. Oral cholestyramine, a resin that is not absorbed, is associated with increased fecal excretion of certain substances, including cholesterol and bile acids. Many patients respond to treatment with cholestyramine with a relief of pruritus, which unfortunately may be temporary, but is well tolerated in general and it seems reasonable to prescribe it as an initial therapy. When pruritus is not relieved by resins, the use of opiate antagonists (eg, naloxone and naltrexone) is supported by data from controlled clinical trials. Butorphanol is an agonist at the kappa opioid receptor and an antagonist at the mu opioid receptor with minimal or absent abuse potential. The use of butorphanol spray in selective patients may be a therapeutic alternative. In uncontrolled observations dronabinol, an agonist at the cannabinoid B1 receptor, and sertraline, a serotonin reuptake inhibitor, have been reported to be associated with the relief of pruritus. The cannabinoidergic and serotoninergic systems participate in the mediation of nociception; therefore, there appears to be a rationale for the use of these drugs to treat pruritus. Data from controlled clinical trials on the use of dronabinol and sertraline, however, are not available at present.

Inhibitory effects of TRK-820 on systemic skin scratching induced by morphine in rhesus monkeys

The inhibitory effects of kappa-opioid receptor agonists on systemic skin scratching induced by the intravenous administration of morphine, a micro-opioid receptor agonist, were investigated in rhesus monkeys. Intravenous pretreatment with kappa-opioid receptor agonists, either TRK-820 at 0.25 and 0.5 microg/kg or U-50488H at 64 and 128 microg/kg, inhibited systemic skin scratching induced by morphine at 1 mg/kg, i.v. in a dose-dependent manner. By the intragastric route, apparent inhibitory effects on morphine-induced systemic skin scratching were evident following pretreatment with TRK-820 at 4 microg/kg but not with U-50488H from 512 to 2048 microg/kg. These results suggest that TRK-820 produces antipruritic effects on i.v. morphine-induced systemic skin scratching and is more readily absorbed intragastrically than is U-50488H, resulting in high bioavailability in the intragastric route.

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

The role of central mu- and kappa-opioid receptors in the regulation of itch sensation was examined using pruritogen-induced mouse scratching behavior model. Intracerebroventricular administration of beta-funaltrexamine, a selective mu-opioid receptor antagonist, inhibited the scratching behavior induced by intradermal substance P, but subcutaneous administration of beta-funaltrexamine did not. Similarly, the scratching inhibitory activity of subcutaneously administered TRK-820, (-)-17-(cyclopropylmethyl)-3, 14beta-dihydroxy-4, 5alpha-epoxy-6beta-[N-methyl-trans-3-(3-furyl) acrylamido] morphinan hydrochloride, a kappa-opioid receptor agonist, was antagonized by intracerebroventricular administration of nor-binaltorphimine (10 microg/site), a kappa-opioid receptor antagonist, but was not by subcutaneous administration of nor-binaltorphimine. In addition, the scratching induced by the direct activation of central mu-opioid receptor by intracisternal morphine was significantly and dose-dependently inhibited by subcutaneous administration of TRK-820. Taken all together, it is suggested that the central mu-opioid receptors play a role in the processing of itch sensation, and the activation of central kappa-opioid receptors antagonize the central mu-opioid receptor mediated itch processing, thereby suppressing itch sensation.

Aerobic exercise: a potential therapeutic intervention for patients with liver disease

Fatigue is a symptom of liver disease. Indirect evidence suggests that this type of fatigue is centrally mediated. Non-alcoholic steatohepatitis (NASH), which may lead to cirrhosis, is associated with insulin resistance. An activated hypothalamic pituitary adrenal axis results in increased secretion of cortisol releasing hormone, cortisol and catecholamines. Prolonged exposure to high levels of cortisol is associated with insulin resistance, as exemplified by the metabolic syndrome. Accumulation in visceral fat is an independent factor associated with insulin resistance. Central (visceral) fat is less sensitive to insulin than the rest of body fat and the central nervous system and not peripheral insulin, appears to regulate lipolysis in visceral fat by, at least in part, adrenergic mechanisms. Aerobic training has documented beneficial effects on mental health and fatigue secondary to chronic illness. In addition, aerobic training increases insulin sensitivity. Thus, aerobic training may decrease fatigue in liver disease and improve NASH.

Pruritus in chronic liver disease: mechanisms and treatment

Pruritus is a complication of liver disease. It can have a marked negative impact on quality of life; when intractable, it is an indication for liver transplantation. The cause of this type of pruritus is unknown. There is, however, evidence to suggest that the pruritus associated with liver disease is mediated, at least in part, by endogenous opioids. A central mechanism has been proposed. Therapeutic interventions have concentrated on the removal of presumed and unknown pruritogens from the circulation, hepatic enzyme induction, and, over the past decade, opiate antagonists, the first specific treatment for the pruritus of cholestasis. Other pharmacologic interventions that change neurotransmission have recently been reported to decrease the pruritus in patients with liver disease, as has a newly developed system that applies albumin-based dialysis. These interventions are promising, but they must be tested in properly controlled behavioral trials.

A study of bile acids as opioid receptor ligands in rat brain membranes

There is evidence to suggest that the pruritus that results from liver disease is mediated, at least in part, by opioid receptor-ligand interactions; a central component has been proposed. Opiate drugs with agonist activity at opioid receptors induce naloxone-reversible pruritus. Bile acids accumulate in tissues in liver disease. We studied the ability of bile acids to displace specific opioid ligands from opioid receptors in rat and guinea pig brain membrane preparation in binding assays. None of the bile acids studied displaced significantly the opioid ligands from their receptors suggesting that bile acids in vitro are not opioid receptor ligands. The results of this study do not support a role of these bile acids as direct pruritogens by an opioid receptor-mediated mechanism.

Benign recurrent intrahepatic cholestasis

Benign recurrent intrahepatic cholestasis is a rare autosomal recessive disorder characterized by repeated episodes of intense pruritus, profound elevations in serum alkaline phosphatase and bilirubin, with normal or nearly normal values for serum gamma-glutamyl transferase. Attack lasts from several weeks to months and resolve spontaneously. Between attacks patients remain asymptomatic for months to years. The disorder does not lead to progressive liver injury and is not fatal. Genetic studies have demonstrated that the disorder is the result of a mutation in ATP8BI, a gene that codes for the FIC1 (familial intrahepatic cholestasis) protein, which is also affected in other forms of familial intrahepatic cholestasis. It is believed this protein plays a role in bile acid secretion, in aminophospholid transport, and in maintaining fluidity of the cell membrane. Therapy is supportive and aimed at relieving pruritus and other complications of severe cholestasis until the episode resolves spontaneously.

An approach to the management of the pruritus of cholestasis

The cause of the pruritus of cholestasis is unknown. It is inferred that pruritus results from the accumulation in plasma of substances that are made in the liver and excreted in bile under physiologic conditions. The idea of neurotransmitters as important mediators in the pruritus of cholestasis has evolved over the past several years. There is evidence to suggest that endogenous opioids contribute to the pruritus of cholestasis and, for the first time, specific treatment for the pruritus has been instituted. The deficiency of studying pruritus with subjective methodology alone has been overcome with the development of objective methodology to study the behavioral manifestation of pruritus, scratching behavior. The use of this tool allows the definition of clear objective end-points, scratching activity, for inclusion in clinical trials.

Pruritus and fatigue in primary biliary cirrhosis

Pruritus and fatigue are the most common symptoms of patients with PBC, and both have marked negative impact on quality of life. Over the past decade, evidence has emerged supporting a role of the central nervous system in the pathogenesis of these two common manifestations of PBC. There is no evidence that the pruritus of cholestasis is mediated in the skin. Clinical and laboratory data do support a role of the opioid neurotransmitter system in the mediation of the pruritus of cholestasis; a central mechanism has been proposed. Treatment with opiate antagonist is thus a specific alternative. Studies of the behavioral consequence of the pruritus of cholestasis, scratching activity, allow for the design of clinical trials with objective end-points. The etiology of fatigue is unknown. A central component is being considered. The identification of objective alterations in fatigue and the adoption of a definition that incorporates the perception and the behavioral consequences of fatigue should facilitate the development of objective methodology. The potential role of various neurotransmitter systems, including the serotonin system and the opioid system, in the mediation of the fatigue of PBC seems to merit further investigation.

The cannabinoid agonist WIN 55, 212-2 increases nociception threshold in cholestatic rats: implications for the treatment of the pruritus of cholestasis

Dronabinol, a synthetic agonist at cannabinoid receptors, was reported to decrease the pruritus of cholestasis, in an uncontrolled observation. We hypothesized that the reported antipruritic effect of dronabinol might have resulted from an increased threshold to experience nociception (i.e. pruritus) by the drug. To test this hypothesis, we studied the effect of WIN 55, 212-2, a cannabinoid agonist, on the threshold to experience nociception, using a tail-flick assay in rats with cholestasis secondary to bile duct resection and in sham-resected controls. The administration of WIN 55, 212-2 was associated with a significant increase in the mean tail-flick latency in both groups as compared to baseline. Pruritus is a nociceptive stimulus; accordingly, drugs that increase the threshold to nociception in human beings may be a novel approach to the treatment of this symptom in patients with liver disease.

Pain as a complication of use of opiate antagonists for symptom control in cholestasis

Controlled trials have suggested that opiate antagonist therapy may be effective for the treatment of the symptoms of cholestasis. The oral opiate antagonist naltrexone in particular has started to enter into routine clinical use for amelioration of cholestatic itch. Attention regarding the side effects of opiate antagonist therapy has, to date, largely focused on an opiate withdrawal-type reaction (which can be controlled effectively by titrated therapy introduction regimens). Here we describe 3 cases of a further clinically important side effect, loss of control of pain resulting from other pathologies, which in each case necessitated the withdrawal of hitherto clinically effective opiate antagonist therapy. Of the 14 patients treated by our unit with opiate antagonist agents for the control of cholestatic symptoms, 13 (93%) showed resolution of, or significant improvement in, symptoms. Of the 13 patients showing a clinical response, 7 (54%) subsequently had to discontinue therapy because of side effects (including the 3 patients with uncontrolled pain). It is our experience that in the routine clinical setting, opiate antagonists are highly effective for the treatment of cholestatic symptoms. In practice, however, their usefulness is limited by their side-effect profile.

Alpha2-adrenoceptor and NO mediate the opioid subsensitivity in isolated tissues of cholestatic animals

1. Our previous report showed that in acute cholestasis, the subsensitivity to morphine inhibitory effect on electrical-stimulated contractions develops significantly faster in guinea-pig ileum (GPI) and in mouse vas deferens (MVD) (45.2 and 29.9 times, respectively) compared with non-cholestatic subjects. 2. The possible contribution of alpha2-adrenoceptor and nitric oxide (NO) pathways on the development of tolerance was assessed in GPI and MVD of cholestatic subjects. 3. Daily administration of naltrexone (20 mg kg(-1)), yohimbine (5 mg kg(-1)), and Nomega-nitro-l-arginine methyl ester (l-NAME) (3 mg kg(-1)) to cholestatic animals significantly (P-value < 0.05) inhibited the process of subsensitivity in all groups. 4. Consistent with the literature, it was concluded that both the alpha2-adrenergic system and NO have close interaction with the opioid system and may underlie some of the mechanisms involved in the subsensitivity development to opioids in acute cholestatic states.

Treatment of pruritus associated with systemic disorders in the elderly: a review of the role of new therapies

Generalised pruritus is common in the elderly. Idiopathic 'senile pruritus' is a diagnosis of exclusion, and an underlying systemic disorder should be sought. Thyroid disease, haematological malignancy, iron deficiency, cholestasis or renal impairment may be responsible for pruritus. Rarely pruritus may occur after cerebral infarction or as a paraneoplastic phenomenon. The mechanisms of pruritus are poorly understood. In systemic disorders, correction of the underlying disorder alleviates itch. However, when this cannot be achieved, a symptomatic approach is required. Response to treatment varies enormously and an empirical approach is often required. Topical applications are available to soothe the skin and bandaging techniques may improve their efficacy. A number of more targeted treatments are available for renal and cholestatic pruritus. Novel therapies such as thalidomide, opioid antagonists, ondansetron and phototherapy with ultraviolet (UV)-B radiation are now being used. Treatment of pruritus needs to be individualised, and the elderly present a particular challenge. Adequate delivery of simple emollients may be impossible because of physical impairment The elderly are more vulnerable to the adverse effects of treatments, comorbidities may alter the pharmacokinetics of drug metabolism and polypharmacy increases the likelihood of adverse drug interactions. Cognitive impairment can lead to poor compliance with treatment. The patient's general health, the severity of symptoms and the adverse effects of treatment all need to be considered. Most treatments are of benefit only to some patients; others derive only marginal improvement. Many of the newer treatments are unlicensed for pruritus and should preferably be administered under specialist supervision. We review the literature concerning the treatment of itch associated with systemic diseases, with particular emphasis on issues relevant to the elderly. Pruritus is a difficult symptom to treat. However, it is hoped that research into the mechanisms underlying the pruritus of systemic disease will allow a better understanding so that we should be able to look forward to more specific and effective therapies in the future.

Review article: pruritus in cholestatic and other liver diseases

Pruritus is often the most troublesome symptom in patients with chronic liver disease, particularly when cholestasis is a prominent feature. The exact pathogenesis is unknown, but empirical treatment, such as cholestyramine, based on a liver-based origin of pruritus, has been used for many years. Recently, evidence for a central mechanism for pruritus has been obtained and opioid antagonists have been tried clinically with some benefit, but their use is not widespread. In addition, the pruritus associated with intrahepatic cholestasis of pregnancy can now be alleviated in many cases by ursodeoxycholic acid. As it also improves foetal outcome, this should become first-line therapy. We review the pathogenesis and therapy of pruritus, highlighting practical aspects to help with patients with seemingly intractable pruritus.

Role of opioid and nitric oxide systems in the nonadrenergic noncholinergic-mediated relaxation of corpus cavernosum in bile duct-ligated rats

Changes in nonadrenergic noncholinergic (NANC)-mediated relaxation of the anococcygeus muscle have been demonstrated in cholestasis. Cholestasis is also associated with accumulation of endogenous opioid peptides and nitric oxide (NO) overproduction. This study was therefore undertaken to investigate the effect of cholestasis on the NANC-mediated relaxation of corpus cavernosum in bile duct-ligated rats and to examine the possible roles of the opioid system and nitric oxide in the cholestasis-associated alterations of corpus relaxation. Bile duct-ligated and sham-operated rats were treated for 2 weeks with either normal saline, N (omega)-nitro L-arginine methylester (L-NAME) (3 mg/kg/day, i.p.) or naltrexone (20 mg/kg/day, i.p.). On the 14th day, the strips of corpus cavernosum were mounted under tension in a standard oxygenated organ bath with guanethidine sulfate (5 microM) and atropine sulfate (1 microM) (to produce adrenergic and cholinergic blockade). The strips were precontracted with phenylephrine hydrochloride (7.5 microM) and electrical field stimulation was applied at different frequencies to obtain NANC-mediated frequency-dependent relaxant responses. The results showed that the amplitudes of relaxation responses at each frequency in bile duct-ligated rats were greater than the responses of sham-operated animals. This increase in relaxation responses in bile duct-ligated rats was inhibited by chronic L-NAME administration for 2 weeks so it seemed that it might be due to the nitric oxide overproduction in cholestatic states. Chronic administration of naltrexone for 2 weeks to bile duct-ligated rats had the same inhibitory effect on the relaxation responses. Our results demonstrated that in cholestasis, there was an increase in NANC-mediated relaxation of corpus cavernosum and both opioid and nitric oxide systems were involved in this increase.

Efficacy and safety of oral naltrexone treatment for pruritus of cholestasis, a crossover, double blind, placebo-controlled study

BACKGROUND/AIMS

To assess the efficacy and safety of naltrexone for the short and long term treatment of pruritus of cholestasis.

METHODS

Twenty patients with pruritus and cholestasis were included. A baseline pruritus score was obtained over 1 week. Patients were then randomized to receive 50 mg/day of naltrexone or placebo for 2 weeks. Subsequently, a 1-week washout period ensued and patients were crossed over to the other therapy for 2 additional weeks. Pruritus was assessed daily with a visual analogue scale (VAS) from 0 to 10. Patients whose pruritus decreased >50% of basal with naltrexone received naltrexone 50 mg/day for 2 additional months.

RESULTS

Mean basal VAS was similar in both groups. VAS showed greater and more significant changes with naltrexone than with placebo (P<0.0003). In nine out of 20 patients (45%) receiving naltrexone, pruritus decreased >50% compared to basal value, including five whose pruritus disappeared completely. No significant changes were observed in serum biochemistry. Most of the adverse events that occurred during the first 48 h of naltrexone therapy were consistent with opioid withdrawal-like phenomena and spontaneously disappeared 2 days after starting treatment.

CONCLUSIONS

Naltrexone can be considered as an alternative option to treat pruritus of cholestasis. In the current study, side effects were transient and did not require specific medication.

Extrahepatic manifestations of cholestasis

Pruritus, fatigue and metabolic bone disease represent three major extrahepatic manifestations of chronic cholestatic liver disease that considerably affect the patient's quality of life. The present article reviews pathogenetic aspects of and current therapeutic approaches to extrahepatic manifestations of cholestatic liver disease. Pathogenesis of pruritus of cholestasis remains poorly understood. The involvement of putative peripherally acting pruritogens, such as bile acids or endogenous opioids, is being discussed. More recently, central mechanisms, including an increased central opioidergic tone and pertubations in the serotonergic system have been proposed. Treatment of the underlying disease is beneficial also for the control of cholestasis-associated pruritus. Current therapeutic recommendations include ursodeoxycholic acid, cholestyramine, rifampicin and opioid antagonists. Liver transplantation may be indicated when severe pruritus is refractory to medical treatment. Fatigue is being recognized as the most frequent and one of the most disabling complaints in chronic cholestasis. Fatigue is presumably of central origin and its association with other neuropsychiatric disorders (e.g. depression, obsessive-compulsive disorders) is consistent with defective central neurotransmission. No specific therapies are currently available and a healthy lifestyle, regular sleep and avoidance of unnecessary stress and other precipiting factors are recommended. Antidepressant therapy may be warranted in selected patients. Osteopenia and osteoporosis are common in chronic cholestatic liver disease, whereas osteomalacia is rare. The pathophysiology of cholestasis-associated metabolic bone disease is regarded as multifactorial. Therapeutic recommendations include regular exercise, calcium and vitamin D supplementation in late stage disease, hormone replacement therapy in postmenopausal women and bisphosphonates.

Do endogenous opioids contribute to the bradycardia of rats with obstructive cholestasis?

Endogenous opioids have nitric oxide (NO)-dependent cardiovascular actions. In the light of biological evidence of accumulation of endogenous opioids in cholestasis and also existence of NO-dependent bradycardia in cholestatic subjects, this study was carried out to evaluate the role of endogenous opioids in the generation of bradycardia in a rat model of cholestasis. Male Sprague-Dawley rats were used to induce cholestasis by surgical ligation of the bile duct, with sham-operated animals serving as a control. The animals were divided into six groups which received naltrexone [20 mg/kg/day, subcutaneously (s.c.)], N(G)-L-nitro-arginine methyl ester (L-NAME, 3 mg/kg/day, s.c.), aminoguanidine (200 mg/kg/day, s.c.), L-arginine (200 mg/kg/day, s.c.), naltrexone + L-NAME (20 and 3 mg/kg/day, s.c) or saline. One week after the operation, a lead II electrocardiogram (ECG) was recorded and the spontaneously beating atria of the animals were then isolated and the chronotropic responses to epinephrine evaluated. The plasma L-nitro-tyrosine level and alanine amino transferase and alkaline phosphatase activities were also measured. The heart rate of cholestatic animals was significantly lower than that of control rats in vivo and this bradycardia was corrected with daily adminstration of naltrexone or L-NAME. The basal spontaneous beating rate of atria in cholestatic animals was not significantly different from that of sham-operated animals in vitro. Cholestasis induced a significant decrease in the chronotropic effect of epinephrine. This effect was corrected by daily injection of naltrexone or L-NAME, or concurrent administration of naltrexone + L-NAME, and was not corrected by aminoguanidine. L-arginine had an equivalent effect to L-NAME and increased the chronotropic effect of epinephrine in cholestatic rats but not in control animals. Bile duct ligation increased the plasma activity of liver enzymes as well as the level of L-nitro-tyrosine. L-arginine and naltrexone treatment significantly decreased the elevation of liver enzymes in bile duct-ligated rats. Pretreatment of cholestatic animals with naltrexone or L-NAME decreased the plasma L-nitro-tyrosine level. The results suggest that either prevention of NO overproduction or protection against liver damage is responsible for recovery of bradycardia after naltrexone administration.

Opioid antagonists: a review of their role in palliative care, focusing on use in opioid-related constipation

Opioid antagonists have well-established indications in the reversal of life-threatening opioid toxicity, but also hold considerable promise for other applications in palliative care practice, particularly management of opioid-related constipation. We briefly review current understanding of opioid receptors, focusing on their complex role in gastrointestinal physiology. We summarize the pharmacology, conventional indications, and clinical usage of three major groups of opioid antagonists, including a promising new peripherally acting agent, methylnaltrexone, which is not commercially available. We suggest an approach to administering opioid antagonists for reduction of life-threatening opioid toxicity in patients with pain. The literature on opioid-induced constipation and its treatment with opioid-antagonists is reviewed in detail. Finally, other potential uses of opioid antagonists in palliative care are described, especially strategies for reducing such opioid side effects as nausea and pruritus and for improving analgesia or reducing tolerance by concomitantly administrating both an opioid agonist and low dosages of an antagonist.

The nonadrenergic noncholinergic relaxation of anococcygeus muscles of bile duct-ligated rats

Previous studies have shown the naloxone-induced withdrawal syndrome and the development of tolerance in the tissues of cholestatic animals. Increased neuronal nitric oxide synthase (nNOS) expression is reported to exist in morphine-tolerant animals. This, together with evidence for nitric oxide (NO) overproduction in cholestasis, suggested the possibility of an alteration of nonadrenergic noncholinergic (NANC) relaxation of anococcygeus muscles of cholestatic rats. To study this, we used three main groups of animals: unoperated, sham-operated and bile duct-ligated. Electrical field stimulation, in the presence of atropine and guanethidine, caused NANC relaxation in the anococcygeus muscle which was enhanced in bile duct-ligated animals. N(G)-nitro-L-arginine methyl ester (L-NAME), a NOS blocker, caused a dose-dependent inhibition of the NANC relaxation. The IC(50)'s of L-NAME in 7-day (7.30+/-0.87 microM), 14-day (6.98+/-0.70 microM) and 21-day (8.25+/-1.40 microM) bile duct-ligated groups were significantly different from those of unoperated (1.69+/-0.30 microM) and sham-operated groups (1.90+/-0.27 microM). L-NAME (100 microM) completely inhibited the NANC relaxation response, suggesting that NANC relaxation in the rat anococcygeus muscle is mediated mainly via NO. The contraction response of the intact muscle to phenylephrine, an alpha(1)-adrenoceptor agonist, and the relaxation response of the phenylephrine-contracted muscle to sodium nitroprusside, an NO donor, were not different in unoperated, sham-operated and 7-day bile duct-ligated groups. These results showed that the smooth muscle component of NANC relaxation is not altered in anococcygeus muscles of bile duct-ligated rats. It can thus be concluded that the NANC relaxation in the anococcygeus of cholestatic rats is more resistant to a NOS blocker, providing evidence for increased nitrergic neurotransmission in the anococcygeus muscles of cholestatic rats.

Hepatic Met-enkephalin immunoreactivity is enhanced in primary biliary cirrhosis

BACKGROUND/AIMS

In contrast to the normal adult liver, the fetal human and rat livers, and the liver of rats with cholestasis secondary to bile duct resection (BDR) express the preproenkephalin (ppENK) mRNA, which codes for the endogenous opioid peptide Met-enkephalin. In addition, Met-enkephalin immunoreactivity (MEIR) is detected in hepatocytes and in proliferating bile ductules in the cholestatic rat liver. These data suggest that cholestasis is associated with the resurgence of cells that produce Met-enkephalin. To explore further the status of opioids in cholestasis, we studied the expression of MEIR in liver tissue.

METHODS

The MEIR was sought in paraffin-preserved liver tissues from patients with primary biliary cirrhosis (PBC) (n = 10).

RESULTS

The MEIR was detected in all the PBC livers. Its intensity varied from weak to strong on hepatocytes and bile ducts and the strongest expression appeared as coarse granules. The MEIR was either absent or only faintly expressed by some hepatocytes from disease and nondisease control biopsies, but absent from bile ducts.

CONCLUSION

These results suggest that the human liver in cholestasis may be a source of endogenous opioids.

Review article: the concept of entero-colonic encephalopathy, autism and opioid receptor ligands

There is growing awareness that primary gastrointestinal pathology may play an important role in the inception and clinical expression of some childhood developmental disorders, including autism. In addition to frequent gastrointestinal symptoms, children with autism often manifest complex biochemical and immunological abnormalities. The gut-brain axis is central to certain encephalopathies of extra-cranial origin, hepatic encephalopathy being the best characterized. Commonalities in the clinical characteristics of hepatic encephalopathy and a form of autism associated with developmental regression in an apparently previously normal child, accompanied by immune-mediated gastrointestinal pathology, have led to the proposal that there may be analogous mechanisms of toxic encephalopathy in patients with liver failure and some children with autism. Aberrations in opioid biochemistry are common to these two conditions, and there is evidence that opioid peptides may mediate certain aspects of the respective syndromes. The generation of plausible and testable hypotheses in this area may help to identify new treatment options in encephalopathies of extra-cranial origin. Therapeutic targets for this autistic phenotype may include: modification of diet and entero-colonic microbial milieu in order to reduce toxin substrates, improve nutritional status and modify mucosal immunity; anti-inflammatory/immunomodulatory therapy; and specific treatment of dysmotility, focusing, for example, on the pharmacology of local opioid activity in the gut.

The additive effect of opioids and nitric oxide in increasing pentylenetetrazole-induced seizure threshold in cholestatic mice

BACKGROUND

Accumulation of endogenous opioids and overproduction of nitric oxide has been reported in cholestatic mice. It is well known that endogenous opioids and nitric oxide alter the susceptibility of experimental animals to different models of seizure.

METHODS

The alterations in clonic seizure thresholds, induced by pentylenetetrazole from 1 to 6 days after bile duct ligation, were evaluated in mice. Whether the pretreatment of cholestatic mice with different doses of opioid receptor antagonist naltrexone, or nitric oxide inhibitor N(omega)-nitro-L-arginine methyl ester would have changed the clonic seizure threshold was also examined.

RESULTS

While in sham-operated mice the clonic seizure threshold was similar to that of the thresholds in unoperated controls, a time-dependent increase in the threshold was observed in cholestatic mice, reaching a peak on day 3 after bile duct ligation and declining partially after the 4th day. Chronic pretreatment with naltrexone (2, 5 and 10 mg/kg, i.p.) reversed the increased threshold in cholestatic mice on day 3 after operation in a dose-dependent manner with the highest doses used restoring the threshold to that of the control animals. A similar reversal of the increased threshold was observed after acute (1, 3 and 10 mg/kg, i.p.) or chronic (10 mg/kg, i.p. for 4 days) pretreatment with N(omega)-nitro-L-arginine methyl ester. Moreover, concurrent administration of doses of N(omega)-nitro-L-arginine methyl ester and naltrexone that each separately induced a partial reversal of increased seizure threshold in cholestasis caused a complete restoring of the threshold to the control level.

CONCLUSIONS

Based on these findings, both opioid receptors and nitric oxide may be involved in the dramatic increase in pentylenetetrazole-induced seizure threshold in cholestasis.

Liver transplantation for intractable pruritus is contraindicated before an adequate trial of opiate antagonist therapy

A woman with stage III (pre-cirrhotic) primary biliary cirrhosis was referred for liver transplantation because of intractable pruritus. Oral administration of 50 mg naltrexone precipitated a severe opioid withdrawal-like reaction. Subsequently, when oral naltrexone therapy was reintroduced following a cautious infusion of naloxone, no reaction occurred and the pruritus resolved completely. Liver transplantation should not be considered for apparently intractable pruritus of cholestasis before an adequate trial of opiate antagonist therapy.

The central opioid system in liver disease and its complications

The best known example of an interaction between the liver and the brain is hepatic encephalopathy. In the 90s a central nervous system origin of the pruritus of cholestatic liver disease and more recently of fatigue of liver disease has been suggested. Hence, three important manifestations of liver disease may be of central origin. Evidence is accumulating that the central opioid system is involved in the development of these manifestations. This short review summarizes current knowledge on the role of the opioid system in development of these liver disease manifestations.

The role of the interaction between endogenous opioids and nitric oxide in the pathophysiology of ethanol-induced gastric damage in cholestatic rats

Interaction between endogenous opioids and nitric oxide (NO) has been shown in different biological models and pharmacological evidence suggest that opioids can induce NO release in endothelium as well as in neural cells. Cholestasis is associated with NO overproduction. The reason for increased NO synthesis is not clearly known but it can potentiate development of gastric mucosal damage in cholestatic subjects. Based on increased plasma levels of endogenous opioids and existence of NO overproduction in cholestasis, the present experiments were performed to investigate the role of interaction between endogenous opioids and NO in generation of ethanol-induced gastric damage in cholestatic rats. Cholestasis was induced by surgical ligation of bile duct and sham-operated rats served as controls. The animals received either 20 mg/kg of naltrexone or saline for 6 days and then were fasted and received L-arginine (200 mg/kg), NG-nitro-L-arginine methylester (L-NAME; 2, 5 and 10 mg/kg) or saline. The ethanol-induced gastric mucosal damage was significantly more severe in cholestatic rats than in sham-operated animals (115 +/- 12 mm2 vs. 72 +/- 11 mm2, P < 0.05). L-NAME significantly enhanced the development of gastric mucosal lesions in sham-operated rats. But in cholestatic animals, L-NAME decreased and L-arginine enhanced the severity of gastric damage. Pretreatment of animals with naltrexone decreased severity of gastric mucosal damage in cholestatic rats. Concurrent administration of naltrexone with L-arginine was protective against ethanol-induced gastric damage in both normal and cholestatic groups. Administration of naltrexone with L-NAME had the same effect in cholestatic and control rats and increased severity of gastric damage. Plasma levels of NO2- + NO3- were significantly higher in cholestatic rats than control animals (72 +/- 6 microM vs. 39 +/- 3 microM, P < 0.05). Pretreatment of animals with naltrexone significantly reduced plasma levels of NO2- + NO3- in cholestatic animals, but not in control rats (33 +/- 6 microM vs. 32 +/- 4 microM). The protective effect of L-NAME against gastric damage in cholestatic rats can be explained by inhibition of NO overproduction and it seems that interaction between opioids and NO may have an important role in generation of NO overproduction and gastric complications in cholestatic rats.

Hepatic encephalopathy

In the last decade, a significant amount of research has been devoted to the pathogenesis and treatment of hepatic encephalopathy (HE). Non-invasive neuroimaging techniques such as magnetic resonance imaging and spectroscopy have become important research tools. The search for a suitable animal model of HE associated with cirrhosis is still ongoing. Moreover, consensus terminology and diagnostic criteria for HE in humans are badly needed.

Neurotropic and psychotropic drugs in dermatology

Several psychotropic and neurotropic agents are useful in treating patients with skin diseases such as obsessive compulsive skin manipulation, delusions of parasitosis, generalized pruritus, and post-herpetic neuralgia. The mechanism of action of these agents is based on their interaction with central and peripheral neuronal receptors. The medications discussed in this article include the tricyclic antidepressants, serotonin reuptake inhibitors, naltrexone, pimozide, and gabapentin. The pharmacology, mechanism of action, adverse effects, drug interactions, and monitoring guidelines are outlined for each of these drugs.

Treatment of primary biliary cirrhosis

Although primary biliary cirrhosis (PBC) is generally a progressive disease, the rate of progression varies greatly from one patient to another. The terminal phase is characterized by hyperbilirubinaemia (>100 micromol/l), a major decrease in the number of intrahepatic bile ducts, and extensive fibrosis or cirrhosis. It is now well established that orthotopic liver transplantation is the treatment of choice for patients entering the terminal phase of the disease.A variety of therapeutic agents have been proposed for treatment of patients with PBC. However, most have been found ineffective or too toxic to be widely used. In contrast, there is accumulating evidence from large therapeutic trials that long-term administration of ursodeoxycholic acid (UDCA) is safe and prolongs survival free of liver transplantation. Treatment with UDCA slows the histological progression and delays the onset of cirrhosis. In patients who have a sub-optimal response to UDCA therapy alone, the combination of colchicine or methotrexate with UDCA has minimal or no additional benefit, whereas that with corticosteroids is more promising but not yet demonstrated. Among causes of non-response to UDCA therapy, the most common is the PBC-autoimmune hepatitis overlap syndrome. The benefit from the combination of corticosteroids and UDCA in this setting is obvious.Further studies are needed to define the patients who are most likely to respond to UDCA therapy and to assess the benefit of combined medical treatments.

The effect of the serotonergic system on opioid withdrawal-like syndrome in a mouse model of cholestasis

There is a marked elevation of endogenous opioid levels in plasma of human subjects with biliary cirrhosis as well as animal model of cholestasis. In addition, development of morphine tolerance and dependence has been shown to be inhibited by drugs which reduce brain serotonin levels. However, intracerebroventricular injection of serotonin increases the morphine analgesia. In the present study we have investigated the role of the serotonergic pathway in determining the withdrawal syndrome in a mouse model of cholestasis. There were three experimental groups: unoperated mice, sham operated mice and mice in which the main bile duct was ligated. Physical dependency was assessed by precipitating a withdrawal syndrome (writing, climbing, rearing, grooming and jumping) by naloxone (2 mg/kg) 5 days after induction of cholestasis. In separate experimental same groups, the antinociception was evaluated by the tail flick latency (TFL) test. Administration of serotonin receptors antagonists, cyproheptadine (10 mg/kg), methysergide (6 mg/kg) and ondansetron (10 mg/kg) attenuated withdrawal signs and decreased the antinociception. However, treatment by fluoxetine (15 mg/kg), an inhibitor of serotonin reuptake, increased the withdrawal signs and antinociception. These experiments lead us to conclude that the naloxone-precipitated withdrawal signs which occur in the mouse model of cholestasis are potentially dependent on the serotonergic pathway. Copyright 2000 John Wiley & Sons, Ltd.

Pruritus and fatigue in primary biliary cirrhosis

Pruritus is experienced by about 80% of patients with primary biliary cirrhosis. It can have a marked negative impact on the quality of life of patients, and it can be an indication for liver transplantation. There is evidence to suggest that the pruritus of cholestasis is mediated, at least in part, by endogenous opioids. A central component has been proposed. Behavioural data have shed light on the pathogenesis of this form of pruritus. Fatigue affects the majority of patients with primary biliary cirrhosis. It interferes with work performance and family life. An idea is emerging that suggests that fatigue in primary biliary cirrhosis also may be mediated centrally. Research tools need to be developed to study fatigue objectively in patients with primary biliary cirrhosis.

Itch-scratch responses induced by opioids through central mu opioid receptors in mice

We examined scratch-inducing effects of intracisternal, intrathecal and intradermal injections of morphine and some opioid agonists in mice. Intracisternal injection of morphine (3 nmol/animal) and the mu-receptor agonist [D-Ala(2), N-Me-Phe(4), Gly(5)-ol]enkephalin (DAMGO; 0.2 nmol/animal) elicited scratching of the face, with little effect on scratching of the trunk. Intracisternal injection of the delta-receptor agonist [D-Pen(2,5)]enkephalin (DPDPE) and the kappa-receptor agonist U50488 were without effects. Intrathecal injection of morphine (0.1-3 nmol/animal) produced a dose-dependent increase in body scratching, with little effects on face scratching. Face scratching induced by intrathecal morphine (3 nmol/animal) was almost abolished by subcutaneous pretreatment with naloxone (1 mg/kg). Intradermal injections of morphine (3-100 nmol/site), DAMGO (1-100 nmol/site), DPDPE (10 and 100 nmol/site) and U50488 (10-100 nmol/site) did not elicit scratching of the site of injection. Intradermal injection of histamine (100 nmol/site) induced the scratching in ICR, but not ddY, mice and serotonin (30 and 50 nmol/site) elicited the scratching in either strain of mice. The results suggest that opioids induce scratching, and probably itching, through central mu-opioid receptors in the mouse.

Management of primary biliary cirrhosis. The American Association for the Study of Liver Diseases practice guidelines

Primary biliary cirrhosis (PBC) is a presumed autoimmune disease of the liver, which predominantly affects women once over the age of 20 years. Most cases are diagnosed when asymptomatic (60%). The antimitochondrial antibody is present in serum in most, but not in all, patients with PBC. The disease generally progresses slowly but survival is less than an age- and gender-matched general population. The symptomatic patient may have fatigue, generalized pruritus, portal hypertension, osteoporosis, skin xanthomata, fat soluble vitamin deficiencies, and/or recurrent asymptomatic urinary tract infections. Many nonhepatic autoimmune diseases are found in association with PBC and may prompt initial presentation. To date, immunosuppressive therapy has not been shown to prolong survival in PBC. The hydrophilic bile acid, ursodeoxycholic acid (UDCA), has been shown when given in a dose of 13 to 15 mg/kg daily for up to 4 years to delay the time to liver transplantation or death. This therapy also causes a significant improvement of all the biochemical markers of cholestasis but has no beneficial effects on any of the symptoms or associated disorders. Treatment with UDCA does not obviate the need for liver transplantation. Therapies to prevent complications arising from malabsorption, portal hypertension, and/or osteoporosis are required as well. Good control of pruritus can be achieved in most patients. PBC is diagnosed with increasing frequency, but the agent(s) responsible for this slowly progressive destruction of the interlobular bile ducts remains elusive and hence a specific therapy remains unavailable.

Effect of NMDA receptor antagonist on naloxone-precipitated withdrawal signs in cholestatic mice

The ability of NMDA antagonist MK-801 to block the expression of opioid-like withdrawal signs was examined in bile duct-ligated mice and the signs were compared with sham operated and unoperated animals. Administration of MK-801 (0/1 mg/kg), 10 min prior to naloxone challenge, significantly reduced the investigated withdrawal signs (jumping, diarrhoea, grooming and climbing) in bile duct-ligated animals. Chronic administration (five consecutive days) of MK-801 (0/1 mg/kg) also decreased all the withdrawal signs in the experimental animals. In an independent series of experiments, the effect of acute and chronic administration of MK-801 on tail-flick latency was investigated in bile duct-ligated animals. Pretreatment with the drug significantly decreased the antinociception induced by bile duct ligation in the mice. The results of this study support evidence for the involvement of the NMDA receptor in yopioidergic-dependent manifestations in a model of obstructive cholestasis. Copyright 2000 John Wiley & Sons, Ltd.

Naltrexone does not relieve uremic pruritus: results of a randomized, double-blind, placebo-controlled crossover study

Improvement of uremic pruritus was reported under short-term administration of the mu-receptor antagonists naltrexone and naloxone. The aim of the present study was to confirm the efficacy and safety of the oral mu-receptor antagonist naltrexone during a 4-wk treatment period in patients on hemodialysis and peritoneal dialysis. A placebo-controlled, double-blind crossover study of uremic patients with persistent, treatment-resistant pruritus was performed. Of 422 patients screened between December 1997 and June 1998, 93 suffered from pruritus and 23 were eligible for the study. Patients were started either with a 4-wk naltrexone sequence (50 mg/d) or matched placebo. This was followed by a 7-d washout, and patients continued with a 4-wk sequence of the alternate medication. Pruritus intensity was scored daily by a visual analogue scale (VAS) and weekly by a detailed score assessing scratching activity, distribution of pruritus, and frequency of pruritus-related sleep disturbance. Sixteen of 23 patients completed the study. During the naltrexone period, pruritus decreased by 29.2% (95% confidence interval [CI], 18.7 to 39.6) on the VAS and by 17.6% (95% CI, 4.2 to 31.1) on the detailed score. In comparison, pruritus decreased by 16.9% (95% CI, 6.8 to 26.9) on the VAS and by 22.3% (95% CI, 9.3 to 35.2) on the detailed score during the placebo period. The difference between the naltrexone and the placebo treatment period was not statistically significant. Nine of 23 patients complained of gastrointestinal disturbances during the naltrexone period compared with only one of 23 patients during the placebo period (P < 0.05). These results show that treatment of uremic pruritus with naltrexone is ineffective. In addition, a high incidence of adverse effects was observed during treatment with naltrexone.