The effect of azelastin hydrochloride on pruritus and leukotriene B4 in hemodialysis patients

Investigational drugs for pruritus

INTRODUCTION

Chronic pruritus (CP), defined as itch lasting for > 6 weeks, is a burdensome symptom of several different diseases, dermatological and systemic, with a high negative impact on the quality of life of patients. Given the manifold aetiologies of CP, therapy is often difficult. In recent years, however, novel substances have been developed for treatment of certain CP entities and identified targets.

AREAS COVERED

In this review, the authors present a survey of targets currently believed to be promising (H4R, IL-31, MOR, KOR, GRPR, NGF, NK-1R, TRP channels) and related investigational drugs that are in the preclinical or clinical stage of development. Some substances have already undergone clinical testing, but only one of them (nalfurafine) has been licensed so far. Many of them are most likely to exert their effects on the skin and interfere there with the cutaneous neurobiology of CP.

EXPERT OPINION

Currently, the most promising candidates for new therapeutic agents in CP are neurokinin-1 receptor antagonists and substances targeting the kappa- or mu-opioid receptor, or both. They have the potential to target the neuronal pathway of CP and are thus of interest for several CP entities. The goal for the coming years is to validate these concepts and move forward in developing new drugs for the therapy of CP.

Evaluation of chronic pruritus in older patients

Chronic pruritus, one of the main symptoms in dermatologic diseases, is often intractable and has a high impact on a patient´s quality of life. In addition to dermatologic disorders, chronic pruritus is associated with systemic and neurologic, as well as psychologic, diseases. Aging skin is considered to be more susceptible to pruritic disorders. Thus, owing to demographic changes, pruritus is becoming more prevalent. The elderly are often afflicted with comorbidities and polypharmacy, which can complicate diagnosis and therapy. In this review we present a rational work-up adapted to the special premises and needs of geriatric patients. This may facilitate the choice of suitable therapeutic regimens.

TRPV1 mediates histamine-induced itching via the activation of phospholipase A2 and 12-lipoxygenase

Histamine provokes itching and is a major skin disease complaint. Histamine is known to excite a subset of sensory neurons, predominantly C-fibers. Although histamine is pruritogenic, its signaling pathways that excite sensory neurons have not been identified. Because the metabolic products of lipoxygenases (LOs) activate transient receptor potential vanilloid receptor-1 (TRPV1) in sensory neurons, we hypothesized that histamine excites sensory neurons by activating TRPV1 via phospholipase A2 (PLA2) and LO stimulation. In cultured sensory neurons, histamine evoked inward currents that were reduced by capsazepine, a TRPV1 blocker. Moreover, histamine provoked inward currents when histamine receptor subtype 1 (H1R) and TRPV1 were expressed heterologously, but not when H1R or TRPV1 was expressed alone. In addition, histamine caused Ca2+ influxes in sensory neurons in wild-type mice but not in TRPV1-/- mice. Furthermore, histamine caused a 2.5-fold increase in the production of 12-hydroxyeicosatetraenoic acid, a metabolite of LO, in cultured sensory neurons. When injected subcutaneously into the necks of mice, histamine caused bouts of scratching, which were greatly reduced by pretreatment with capsazepine, a TRPV1 blocker, and by inhibitors of PLA2, LO, and H1R. Furthermore, mice lacking TRPV1 markedly reduced histamine-induced scratching compared with wild type. Together, these results indicate that TRPV1 plays a key role in mediating the pruritogenic action of histamine via the PLA2/LO pathway.

Suppression by bepotastine besilate of substance P-induced itch-associated responses through the inhibition of the leukotriene B4 action in mice

Anti-pruritic effects of the antihistamine bepotastine besilate were studied in mice. Bepotastine besilate (10 mg/kg) inhibited scratching induced by an intradermal injection of histamine (100 nmol/site), but not serotonin (100 nmol/site). Bepotastine besilate (1-10 mg/kg, oral) dose-dependently suppressed scratching induced by substance P (100 nmol/site) and leukotriene B(4) (0.03 nmol/site). An intradermal injection of substance P (100 nmol/site) increased the cutaneous concentration of leukotriene B(4), which was not affected by bepotastine besilate (10 mg/kg, oral). Leukotriene B(4) increased Ca(2+) concentration in cultured neutrophils, which was suppressed by bepotastine besilate (1-100 microM). Leukotriene B(4) increased Ca(2+) concentration in cultured dorsal root ganglion neurons, which was also suppressed by bepotastine besilate (100 microM). The results suggest that the inhibition of the actions of leukotriene B(4) as well as histamine is involved in the anti-pruritic effect of bepotastine besilate.

Uremic pruritus: a review

Pruritus is a major disorder among the skin derangements in advanced renal failure. Its prevalence seems to be diminishing perhaps because of improvements in dialysis treatment. Recent information suggests that interactions between dermal mast cells and distal ends of nonmyelinated C fibers may be important in the precipitation and regulation of the sensory stimuli. The knowledge as to the control of pruritus transmission to cortex areas is still incomplete but endogenous opioid and opioid receptors may have a role in this regard. A recent classification was proposed for pruritus based on the level of its origin. Uremic pruritus, however, seems to be too complex to fit perfectly in any of the suggested modalities. Inflammation and malnutrition are recognized risk factors for cardiovascular death in end-stage renal disease patients, which may be related to the genesis of pruritus. Consistent with this concept, lower serum levels of albumin and higher serum levels of ferritin were found in pruritic patients when compared to nonpruritic ones. Newer treatments for this difficult clinical problem are being developed and tested.

Turkish Tombul hazelnut (Corylus avellana L.). 2. Lipid characteristics and oxidative stability

The quality of crude hazelnut oil extracted from Tombul (Round) hazelnut, grown in the Giresun province of Turkey, was determined by measuring lipid classes, fatty acids, and fat soluble bioactives (tocopherols and phytosterols). Oxygen uptake, peroxide value, thiobarbituric acid reactive substances, and alpha-tocopherol levels of stripped and crude hazelnut oils in bulk and oil-in-water (o/w) emulsion systems were also evaluated as indices of lipid oxidation over a 21 day storage period at 60 degrees C in the dark. The total lipid content of Tombul hazelnut was 61.2%, of which 98.8% were nonpolar and 1.2% polar constituents. Triacylglycerols were the major nonpolar lipid class and contributed nearly 100% to the total amount. Phosphatidylcholine, phosphatidylethanolamine, and phosphatidylinositol were the most abundant polar lipids, respectively. Sixteen fatty acids were identified, among which oleic acid contributed 82.7% to the total, followed by linoleic, palmitic, and stearic acids. Unsaturated fatty acids accounted for 92.2% of the total fatty acids present. Among oil soluble bioactives, alpha-tocopherol (38.2 mg/100 g) and beta-sitosterol (105.5 mg/100 g) were predominant in hazelnut oil and comprised 88 and 93% of the total tocopherols and phytosterols present, respectively. The results also showed that both stripped and crude hazelnut oils were more stable in terms of lipid oxidation in the bulk oil as compared to those in an o/w emulsion.

Inhibitory effect of azelastine on allergic itch-associated response in mice sensitized with mosquito salivary glands extract

We examined whether azelastine would inhibit itch-associated responses of mice to mosquito allergy. Repeated injections of mosquito salivary gland extract increased scratching and sensory nerve activity. Azelastine inhibited the increased scratching and nerve activity, while terfenadine was without effects. Dexamethasone did not affect the increased scratching. Azelastine suppressed high K(+)-induced increase in intracellular free Ca(2+) in primary cultures of mouse sensory neurons. Direct inhibition by azelastine of sensory neurons may be at least involved in the anti-pruritic effect of azelastine. Histamine, substance P, and leukotriene B(4) may not play a key role in the itching of mosquito allergy.

Inhibitory effects of azelastine on substance P-induced itch-associated response in mice

The anti-pruritic mechanisms of azelastine were studied in mice. Scratching induced by intradermal histamine was inhibited by azelastine (30 mg/kg) and chlorpheniramine (30 mg/kg). Substance P-induced scratching was dose dependently suppressed by azelastine (3-30 mg/kg), but not by chlorpheniramine (10 and 30 mg/kg). Azelastine (30 mg/kg) inhibited the substance P-induced production of leukotriene B4, but not prostaglandin E2, in the skin. Azelastine (3-30 mg/kg) suppressed scratching induced by intradermal injection of leukotriene B4. The results suggest that inhibition of the production and action of leukotriene B4, as well as an anti-histamine action, is involved in the anti-pruritic action of azelastine.

Pathophysiology of pruritus in atopic dermatitis: an overview

Pruritus is an essential feature of atopic dermatitis (AD) and the diagnosis of active AD cannot be made without the history of itching. Because of the high impact on life quality, most of the patients measure the severity of eczema by the intensity of pruritus rather than appearance of skin lesions. However, although pruritus is a cardinal symptom of AD, its mechanism and association with the cutaneous nervous system is not completely understood. Recently, a considerable progress has been achieved in clarifying the complex pathophysiology of pruritus in AD. As a cutaneous sensory perception, itch requires excitation of neuropeptide-containing free nerve endings of unmyelinated nociceptor fibers. It is well known that histamine and acetylcholine provoke itch by direct binding to 'itch receptors' and several mediators such as neuropeptides, proteases or cytokines indirectly via histamine release. Interestingly, some variations of these complex mechanisms could be demonstrated in patients with AD. This review highlights the recent knowledge of different mechanisms which may be involved in regulating pruritus in patients with AD potentially leading to new therapeutic applications for the treatment of itch in AD.

Involvement of leukotriene B(4) in substance P-induced itch-associated response in mice

Intradermal injection of substance P elicits an itch sensation in human subjects and an itch-associated response in mice. The substance P-induced itch-associated response in mice is not inhibited by antihistamine. Therefore, the mechanisms of substance P-induced itch-associated response are unclear. In this study, we demonstrated one of the mechanisms. Substance P induces an arachidonate cascade to produce prostaglandins and leukotriene. In this study we considered whether arachidonate metabolites are involved in the substance P-induced itch-associated response. A phospholipase A(2) inhibitor arachidoryltrifluoromethyl ketone inhibited the substance P-induced itch-associated response in mice. Pre treatment with the glucocorticoids betamethasone and dexamethasone also produced inhibition of the substance P-induced itch-associated response in mice as well as humans. The 5-lipoxygenase inhibitor zileuton, but not the cyclooxygenase inhibitors indomethacin and diclofenac, suppressed substance P-induced itch-associated response. The leukotriene B(4) receptor antagonist 5-[2-(2-carboxyethyl)-3-[6-(4-methoxyphenyl)-5E-hexenyl]oxyphenoxy]valeric acid produced inhibition, whereas pranlukast (leukotriene C(4)/D(4)/E(4) receptor antagonist) and 5(Z)-7-[1S,2S, 3S,5R-3-(trans-b-styren)sulfonamido-6,6-dimethylbi cyclo(3,1,1)hept-2-yl]-5-heptenoic acid (EP(1) receptor antagonist) were without effect. Furthermore, when the production of leukotriene B(4) and prostaglandin E(2) was measured in skin injected with substance P and in mouse keratinocytes applied with substance P, the level of both products increased. As leukotriene B(4), but not prostaglandin E(2), also induces the itch-associated response in mice, these results suggest that leukotriene B(4) and keratinocytes, cutaneous cells which produced leukotriene B(4), play an important role in substance P-induced itch-scratch response in mice. Leukotriene B(4) receptor antagonist and 5-lipoxygenase inhibitor may be novel antipruritic drugs.

Understanding pruritus in systemic disease

Many pruritic conditions do not originate in the skin, but are the result of systemic abnormality. Among the diseases that can cause pruritus are renal insufficiency, cholestasis, Hodgkin's lymphoma, polycythemia vera, solid tumors, and many others. Other pruritic conditions appear to be iatrogenic; opioid-induced pruritus may be the most important in palliative medicine. Successful treatment of the underlying condition usually relieves itch. But, with time, many diseases progress and treatment of the cause will be impossible. Topical treatments may be of limited value. Strategies involving systemic treatments include use of antidepressants, oral opioid antagonists, or cholestyramine. There is no one cure for all pruritic symptoms. Better understanding of mechanisms of pruritus may help develop better treatments.

Evaluation of the onset and duration of effect of azelastine eye drops (0.05%) versus placebo in patients with allergic conjunctivitis using an allergen challenge model

OBJECTIVE

The trial evaluated the effectiveness of the investigational antihistaminic and antiallergic compound Azelastine Eye Drops (AZE) in the treatment of allergic conjunctivitis using an allergen challenge model.

DESIGN

Randomized, double-blind, placebo-controlled, paired-eye study.

PARTICIPANTS

Adults with a history of allergic conjunctivitis (>/=2 years) who were asymptomatic throughout the trial, had a positive skin test (cat dander, grass, or ragweed pollen within the last year), and had a positive conjunctival reaction (score 2+ or more for itching and redness in both eyes on a 0-4 scale) during two separate conjunctival provocation tests (CPT) before randomization.

METHODS

Eighty patients underwent a 2-week screening period (visits 1 and 2) that included a CPT during visit 1 to establish the allergen threshold dose and a second confirmatory CPT performed at visit 2. Eye symptom assessments for itching (evaluated by patient) and conjunctival redness (evaluated by physician) were performed 5 and 10 minutes after CPT using a 5-point scale (from 0 = none to 4+ = severe). Qualified patients were randomized to receive one drop of AZE (0.015 mg of azelastine hydrochloride) in one eye and one drop of placebo in the other eye 20 minutes before CPT at visit 3 (onset) and 8 or 10 hours before CPT at visit 4 (duration).

MAIN OUTCOME MEASURES

Individual severity scores for itching (evaluated by patient) and conjunctival redness (evaluated by physician) for each eye at 3, 5, and 10 minutes after CPT at visits 3 and 4 using a 5-point scale (0 = none to 4+ = very severe).

RESULTS

Each of the 80 randomized patients completed the trial. Mean itching and conjunctival redness scores at visit 3 (onset) were significantly lower (P: < 0.001) in the AZE-treated eyes than in the placebo-treated eyes. At visit 4 (duration), mean itching and conjunctival redness scores (P: </= 0.003) for the 8-hour group and mean itching scores (P: </= 0.001) for the 10-hour group were significantly lower in the AZE-treated eyes than in the placebo-treated eyes. Significant differences in mean tearing and chemosis severity scores were also seen at visit 3 (onset) and visit 4 (duration) in the AZE-treated eyes when compared with the placebo-treated eyes. Treatment with AZE was well tolerated.

CONCLUSIONS

Therapy of experimentally induced allergic conjunctivitis with AZE was highly effective, with an onset of action seen within 3 minutes and a duration of effect of at least 8 to 10 hours.

Involvement of blockade of leukotriene B(4) action in anti-pruritic effects of emedastine in mice

The anti-pruritic activity of emedastine difumarate was studied in mice. Emedastine (0.03-0.3 mg/kg) inhibited scratching induced by intradermal injection of histamine (100 nmol/site). Scratching induced by substance P (100 nmol/site) and leukotriene B(4) (0.03 nmol/site), but not by serotonin (100 nmol/site), was also suppressed by emedastine (0.03-0.3 mg/kg). Intradermal injection of substance P increased the cutaneous concentration of leukotriene B(4), which was not affected by emedastine. These results suggest that the inhibition by emedastine of substance P-induced itch-associated response is mediated by the blockade of leukotriene B(4) action. Anti-leukotriene B(4) action, as well as the anti-histamine action, may contribute to the anti-pruritic effects of emedastine.

Intradermal leukotriene B4, but not prostaglandin E2, induces itch-associated responses in mice

The itch-associated responses induced by intradermal injection of leukotriene B4 and prostaglandin E2 were studied in mice. Leukotriene B4(0.001-1 nmol/site) elicited scratching of the injected site; the dose-response curve was bell-shaped with a peak effect at 0.03 nmol/site. The effect of leukotriene B4 (0.03 nmol/site) started within 3 min, peaked in the second 10-min period, had almost subsided by 30 min, and was inhibited by the simultaneous injection of the leukotriene B4 receptor antagonist ONO-4057, 5-[2-(2carboxyethyl)-3-(6-( p-methoxyphenyl)-5E-hexenyl) oxyphenyoxy] valeric acid. Prostaglandin E2 (0.003-300 nmol/site) did not significantly elicit scratching. The results raise the possibility that leukotriene B4 is an endogenous itch mediator in the skin.