The noncompetitive antagonism of histamine H1 receptors expressed in Chinese hamster ovary cells by olopatadine hydrochloride: its potency and molecular mechanism

Epinastine Cream: A Novel Once-Daily Therapeutic Agent for Allergic Conjunctivitis

Purpose: To investigate the in vivo efficacy of epinastine cream in type I allergic models. Methods: The dose, timing, and antiallergic effect of epinastine cream on the conjunctiva were evaluated postapplication to the eyelid skin of guinea pigs with histamine- or ovalbumin-induced allergic conjunctivitis. Additionally, we assessed its antiallergic effects on the skin postapplication to the dorsal skin of guinea pigs with ovalbumin-induced passive cutaneous anaphylaxis. Efficacy was estimated by determining the amount of dye that leaked from conjunctival or dorsal skin tissue vessels as a measure of vascular permeability, scoring the severity of allergic symptoms, and observing the scratching behaviors using clinical parameters. Results: In the histamine-induced conjunctivitis model, epinastine cream strongly inhibited conjunctival vascular permeability in a dose-dependent manner. The inhibitory effect of 0.5% epinastine cream 24 h postapplication was significantly higher than that of 0.1% epinastine hydrochloride ophthalmic solution 8 h postadministration. Additionally, the 0.5% epinastine cream inhibited conjunctival vascular permeability 15 min postapplication, and the effect was sustained over 24 h. Furthermore, the 0.5% epinastine cream effectively suppressed clinical symptom scores and exhibited ameliorated scratching bouts in conjunctival allergic reactions in the experimental allergic conjunctivitis model. Additionally, it significantly inhibited vascular permeability in skin allergic reactions in the passive cutaneous anaphylaxis model. Conclusions: The results suggest that epinastine cream is a strong, long-lasting, and skin-penetrating inhibitor of type I allergic reactions. The 0.5% epinastine cream applied once daily could be a promising, potent, and long-acting therapeutic agent for allergic conjunctivitis.

The Skeletal Muscle Relaxer Cyclobenzaprine Is a Potent Non-Competitive Antagonist of Histamine H1 Receptors

Cyclobenzaprine is a tricyclic dimethylpropanamine skeletal muscle relaxant, which is used clinically to decrease muscle spasm and hypercontractility, as well as acute musculoskeletal pain. Although the absolute mechanism of action of cyclobenzaprine remains elusive, it is known to mediate its effects centrally via inhibition of tonic somatic motor function, likely through modulation of noradrenergic and serotonergic systems. While cyclobenzaprine is effective as a muscle relaxant, greater than 30% of patients experience drowsiness and sedative-hypnotic effects, yet the mechanisms that cause this adverse effect are also undescribed. Based on this common adverse effect profile and the structural similarity of cyclobenzaprine to tricyclic antidepressants, as well as ethanolamine first-generation antihistamines, we hypothesized that cyclobenzaprine facilitates sedative effects via off-target antagonism of central histamine H1 receptors (H1Rs). Here, for the first time, we present data that demonstrate that cyclobenzaprine exhibits low nanomolar affinity for the cloned human H1R, as well as that expressed in both rat and mouse brain. Using saturation radioligand binding, we also demonstrate that cyclobenzaprine binds to the H1R in a noncompetitive manner. Similarly, functional assays measuring both Ca+2 influx and novel TRUPATH G-protein subunit bioluminescence resonance energy transfer biosensors reveal that cyclobenzaprine also blocks histamine-mediated H1R functional activity in a noncompetitive manner, whereas the classical H1R antagonist diphenhydramine does so competitively. Given that cyclobenzaprine readily crosses the blood-brain barrier and its muscle relaxant effects occur centrally, our data suggest that off-target central antagonism of H1R by cyclobenzaprine facilitates the significant sedative effect of this agent seen in patients. SIGNIFICANCE STATEMENT: Cyclobenzaprine, a clinically used muscle relaxant that is strongly linked to sedation, demonstrates high-affinity noncompetitive antagonism at the histamine H1 receptor. This effect likely modulates the high degree of sedation that patients experience.

Antihistamines for Allergic Rhinitis Treatment from the Viewpoint of Nonsedative Properties

Antihistamines targeting the histamine H₁ receptor play an important role in improving and maintaining the quality of life of patients with allergic rhinitis. For more effective and safer use of second-generation drugs, which are recommended by various guidelines, a classification based on their detailed characteristics is necessary. Antihistamines for first-line therapy should not have central depressant/sedative activities. Sedative properties (drowsiness and impaired performance) are associated with the inhibition of central histamine neurons. Brain H₁ receptor occupancy (H₁RO) is a useful index shown to be correlated with indices based on clinical findings. Antihistamines are classified into non-sedating (<20%), less-sedating (20–50%), and sedating (≥50%) groups based on H₁RO. Among the non-sedating group, fexofenadine and bilastine are classified into “non-brain-penetrating antihistamines” based on the H₁RO. These two drugs have many common chemical properties. However, bilastine has more potent binding affinity to the H₁ receptor, and its action tends to last longer. In well-controlled studies using objective indices, bilastine does not affect psychomotor or driving performance even at twice the usual dose (20 mg). Upon selecting antihistamines for allergic rhinitis, various situations should be taken into our consideration. This review summarizes that the non-brain-penetrating antihistamines should be chosen for the first-line therapy of mild allergic rhinitis.

Efficacy of olopatadine versus epinastine for treating allergic conjunctivitis caused by Japanese cedar pollen: a double-blind randomized controlled trial

Introduction

The objective of this study was to compare the efficacy and safety of olopatadine versus epinastine in healthy Japanese adults with a history of allergic conjunctivitis to Japanese cedar pollen.

Methods

This Phase IV double-blind randomized controlled clinical trial comprised three clinical visits over 30 days. Screening tests were performed to identify subjects with a history of allergic conjunctivitis to Japanese cedar pollen in terms of skin sensitivity and positive bilateral reactions to a conjunctival allergen challenge (CAC) with Japanese cedar pollen at Visit 1, and confirmation by a positive bilateral CAC reaction at Visit 2. At Visit 3, the subjects were randomized to receive one drop of olopatadine HCl ophthalmic solution 0.1% (olopatadine) in the left or right eye (1:1 ratio). All subjects received one drop of epinastine HCl ophthalmic solution 0.05% (epinastine) in the contralateral eye as an active control. Five min later, the subjects underwent bilateral CAC tests with one drop of the allergen solution at the concentration that elicited positive reactions at Visits 1 and 2. Efficacy outcomes included the severity of ocular itching at 5, 7, and 15 min and the severity of conjunctival hyperemia at 7, 15, and 20 min after the CAC test, as graded by the investigator by biomicroscopy.

Results

Fifty people participated in this study (25 per group). Olopatadine significantly reduced ocular itching at 7 and 15 min (both p < 0.05) and conjunctival hyperemia at 7 and 20 min (p = 0.0010 and p < 0.05, respectively) after allergen exposure compared with epinastine. There were no adverse events for either treatment.

Conclusion

The results of this single-dose study suggest that olopatadine is superior to epinastine in terms of suppressing ocular itching and hyperemia induced by Japanese cedar pollen during CAC tests. Further studies are needed to confirm these findings in real-life settings.

Electronic supplementary material

The online version of this article (doi:10.1007/s12325-014-0156-2) contains supplementary material, which is available to authorized users.

Internalization of CCR4 and inhibition of chemotaxis by K777, a potent and selective CCR4 antagonist

CC chemokine receptor 4 (CCR4) is a G protein-coupled receptor that regulates the chemotaxis of Th2 lymphocytes, which are key players in allergic diseases. K777 is a small compound identified in a binding assay using a CCR4 ligand, CCL17. K777 inhibited both CCL17 binding and CCL17-induced chemotaxis in Hut78 cells (IC50: 57 and 8.9 nmol/l, respectively). The K777-mediated inhibition of chemotaxis was potent even in the presence of a 10-fold higher concentration of CCL17. The imaging and flow cytometric analyses revealed that K777 induced CCR4 internalization, with a ∼50% reduction of cell surface CCR4. K777 did not inhibit CXCR4-induced chemotaxis or internalization and did not bring about Ca(2+) mobilization by itself. A Scatchard plot analysis of the binding assay using radiolabeled K777 revealed a single high-affinity binding site on the CCR4 molecule. These results indicate that K777 is a selective CCR4 antagonist featuring the potent chemotaxis inhibition, to which the internalization-inducible ability of K777 to hide a part of cell surface CCR4 may contribute.

Effects of single therapeutic doses of promethazine, fexofenadine and olopatadine on psychomotor function and histamine-induced wheal- and flare-responses: a randomized double-blind, placebo-controlled study in healthy volunteers

Since most first-generation antihistamines have undesirable sedative effects on the central nervous systems (CNS), newer (second-generation) antihistamines have been developed to improve patients’ quality of life. However, there are few reports that directly compare the antihistaminic efficacy and impairment of psychomotor functions. We designed a double-blind, placebo controlled, crossover study to concurrently compare the clinical effectiveness of promethazine, a first-generation antihistamine, and fexofenadine and olopatadine, second-generation antihistamines, by measuring their potency as peripheral inhibitors of histamine-induced wheal and flare. Further, we investigated their sedative effects on the CNS using a battery of psychomotor tests. When single therapeutic doses of fexofenadine (60 mg), olopatadine (5 mg) and promethazine (25 mg) were given in a double-blind manner to 24 healthy volunteers, all antihistamines produced a significant reduction in the wheal and flare responses induced by histamine. In the comparison among antihistamines, olopatadine showed a rapid inhibitory effect compared with fexofenadine and promethazine, and had a potent effect compared with promethazine. In a battery of psychomotor assessments using critical flicker fusion, choice reaction time, compensatory tracking, rapid visual information processing and a line analogue rating scale as a subjective assessment of sedation, promethazine significantly impaired psychomotor function. Fexofenadine and olopatadine had no significant effect in any of the psychomotor tests. Promethazine, fexofenadine and olopatadine did not affect behavioral activity, as measured by wrist actigraphy. These results suggest that olopatadine at a therapeutic dose has greater antihistaminergic activity than promethazine, and olopatadine and fexofenadine did not cause cognitive or psychomotor impairment.

Structure of the human histamine H1 receptor complex with doxepin

The biogenic amine histamine is an important pharmacological mediator involved in pathophysiological processes such as allergies and inflammations. Histamine H(1) receptor (H(1)R) antagonists are very effective drugs alleviating the symptoms of allergic reactions. Here we show the crystal structure of the H(1)R complex with doxepin, a first-generation H(1)R antagonist. Doxepin sits deep in the ligand-binding pocket and directly interacts with Trp 428(6.48), a highly conserved key residue in G-protein-coupled-receptor activation. This well-conserved pocket with mostly hydrophobic nature contributes to the low selectivity of the first-generation compounds. The pocket is associated with an anion-binding region occupied by a phosphate ion. Docking of various second-generation H(1)R antagonists reveals that the unique carboxyl group present in this class of compounds interacts with Lys 191(5.39) and/or Lys 179(ECL2), both of which form part of the anion-binding region. This region is not conserved in other aminergic receptors, demonstrating how minor differences in receptors lead to pronounced selectivity differences with small molecules. Our study sheds light on the molecular basis of H(1)R antagonist specificity against H(1)R.

Pre-seasonal treatment with topical olopatadine suppresses the clinical symptoms of seasonal allergic conjunctivitis

PURPOSE

To evaluate the effectiveness of pre-seasonal treatment with topical olopatadine on the reduction of clinical symptoms of seasonal allergic conjunctivitis (SAC).

DESIGN

Prospective interventional case series.

METHODS

Eleven patients with SAC received topical olopatadine in one eye at least two weeks before the onset of allergy symptoms, and the other eye served as the control. After the onset of allergic conjunctivitis, both eyes were treated with topical olopatadine. Visual analogue scale (VAS), which evaluated the subjective symptoms of ocular allergy, and the tear levels of histamine and substance P were measured up to six weeks.

RESULTS

At the onset of allergy symptoms, the VAS score in the pretreatment eyes was statistically significantly lower than that in the control eyes. The VAS score in the control eyes decreased with time but did not decrease to the level seen in the pretreatment eyes until four weeks later. The tear level of substance P at the onset of allergy symptoms was significantly suppressed in the pretreatment eyes, while the level of histamine was not suppressed. Alteration of the VAS scores in the pretreatment eyes significantly correlated with the level of substance P, but not of histamine.

CONCLUSIONS

To suppress clinical symptoms in patients with SAC, pre-seasonal treatment with topical olopatadine is effective. The effectiveness of treatment correlates with the tear level of substance P.

Effects of olopatadine hydrochloride, a histamine h(1) receptor antagonist, on histamine-induced skin responses

Effects of olopatadine hydrochloride, a histamine H₁ receptor antagonist, on histamine-induced skin responses were evaluated in 10 healthy subjects in comparison with placebo, fexofenadine hydrochloride, and bepotastine besilate. Olopatadine significantly suppressed histamine-induced wheal, flare, and itch, starting 30 minutes after oral administration. Olopatadine was more effective than fexofenadine and bepotastine. None of the drugs studied impaired performance of word processing tasks. These results suggest that olopatadine can suppress skin symptoms caused by histamine soon after administration.

Evaluation of the antihistamine effects of olopatadine, cetirizine and fexofenadine during a 24 h period: a double-blind, randomized, crossover, placebo-controlled comparison in skin responses induced by histamine iontophoresis

Potency of the antihistamine effects of olopatadine, cetirizine and fexofenadine in standard-dose application were compared from 11.5 to 24 h after application. The test was designed in a double-blind, randomized, crossover, placebo-controlled study of ten healthy volunteers on histamine-induced flare and wheal response using an iontophoresis technique. The suppressive effect of olopatadine on the wheals induced by a 0.1-mA histamine iontophoresis lasted for 24 h after dosing. Fexofenadine administered using the same regimen was the least effective among three drugs tested. Suppression of the wheal response by cetirizine, taken once-daily, decreased with time. Olopatadine completely suppressed even the wheal response induced by a 0.2-mA histamine iontophoresis, although fexofenadine and cetirizine were less effective on the wheals induced by the same histamine challenge. There were no significant differences in subjective drowsiness and objective cognitive function between drug- and placebo-treated subjects. These results demonstrate that olopatadine is the most potent antihistamine among the three H(1)-blockers when administered in a standard dosage.