The expression of functionally-coupled B2-bradykinin receptors in human corneal epithelial cells and their pharmacological characterization with agonists and antagonists

Discovery to Launch of Anti-allergy (Emadine; Patanol/Pataday/Pazeo) and Anti-glaucoma (Travatan; Simbrinza) Ocular Drugs, and Generation of Novel Pharmacological Tools Such as AL-8810

The eye and eyesight are exquistly designed and are precious, and yet we often take them for granted. Good vision is critical for our long-term survival and for humanity's enduring progress. Unfortunately, since ocular diseases do not culminate in life-and-death scenarios, awareness of the plight of millions of people suffering from such eye ailments is not publicized as other diseases. However, losing eyesight or falling victim to visual impairment is a frightening outlook for most people. Glaucoma, a collection of chronic optic neuropathies, of which the most prevalent form, primary open-angle glaucoma (POAG), is the second leading cause of irreversible blindness. POAG currently afflicts >70 million people worldwide and is an insidious, progressive, silent thief of sight that is asymptomatic. On the other hand, allergic conjunctivitis (AC), and the associated rhinitis ("hay-fever"), frequently victimizes a huge number of people worldwide, especially during seasonal changes. While not life-threatening, sufferers of AC soon learn the value of drugs to treat their signs and symptoms of AC as they desire rapid relief to overcome the ocular itching/pain, redness, and tearing AC causes. Herein, I will describe the collective efforts of many researchers whose industrious, diligent, and dedicated team work resulted in the discovery, biochemical/pharmacological characterization, development and eventual launch of drugs to treat AC (e.g., olopatadine [Patanol/Pataday/Pazeo] and emedastine [Emedine]), and for treating ocular hypertension and POAG (e.g., travoprost [Travatan ] and Simbrinza). This represents a personal perspective.

Utilizing Designed Receptors Exclusively Activated by Designer Drug Chemogenetic Tools to Identify Beneficial G Protein-Coupled Receptor Signaling for Fibrosis

Fibrosis or accumulation of extracellular matrix is an evolutionarily conserved mechanism adopted by an organism as a response to chronic injury. Excessive fibrosis, however, leads to disruption of organ homeostasis and is a common feature of many chronic diseases. G protein-coupled receptors (GPCRs) are important cell signaling mediators and represent molecular targets for many Food and Drug Administration-approved drugs. To identify new targets for fibrosis, we used a synthetic GPCR system named designed receptors exclusively activated by designer drugs (DREADDs) to probe signaling pathways essential for fibrotic response. We found that upon expression in human lung fibroblasts, activation of Gq- and Gs-DREADDs abrogated the induction of TGFβ-induced fibrosis marker genes. Genome-wide transcriptome analysis identified dysregulation of multiple GPCRs in lung fibroblasts treated with TGFβ To investigate endogenous GPCR modulating TGFβ signaling, we selected 13 GPCRs that signal through Gq or Gs and activated them by using specific agonists. We examined the impact of each agonist and how activation of endogenous GPCR affects TGFβ signaling. Among the agonists examined, prostaglandin receptor agonists demonstrated the strongest inhibitory effect on fibrosis. Together, we have demonstrated that the DREADDs system is a valuable tool to identify beneficial GPCR signaling for fibrosis. This study in fibroblasts has served as a proof of concept and allowed us to further develop in vivo models for fibrosis GPCR discovery. SIGNIFICANCE STATEMENT: Fibrosis is the hallmark of many end-stage cardiometabolic diseases, and there is an unmet medical need to discover new antifibrotic therapies, reduce disease progression, and bring clinically meaningful efficacy to patients. Our work utilizes designed receptors exclusively activated by designer drug chemogenetic tools to identify beneficial GPCR signaling for fibrosis, providing new insights into GPCR drug discovery.

Bradykinin potentially stimulates cell proliferation in rabbit corneal endothelial cells through the ZO‑1/ZONAB pathway

Bradykinin (BK) has been demonstrated to induce proliferation in several types of cell in ex vivo corneas. However, the mechanisms underlying the action of BK on corneal endothelial cells (CECs) remain largely unknown. The present study aimed to investigate the effect of BK on rabbit corneal endothelial cell (RCEC) proliferation, and assess the involvement of the zonula occludens‑1(ZO‑1)/ZO‑1associated nucleic acid binding protein (ZONAB) pathway. Cell proliferation and cell cycle distribution was analyzed following treatment with BK (0.01, 0.1,1.0 or 10.0 µM) for the indicated time intervals (24, 48, 72 and 96 h), or following BK treatment combined with transfection of ZONAB‑small interfering (si)RNA for 72 h. In addition, the expression of tight junction ZO‑1, nuclear ZONAB, proliferating cell nuclear antigen(PCNA) and cyclin D1 were evaluated using western blotting or immunofluorescence. BK treatment was demonstrated to induce time‑ and concentration‑dependent cell proliferation and cell cycle progression, along with the upregulation of tight junction ZO‑1 and nuclear ZONAB, as well as PCNA and cyclin D1 protein expression. Furthermore, knockdown with ZONAB‑siRNA inhibited cell proliferation, induced cell cycle arrest and downregulated PCNA and cyclin D1 protein expression. ZONAB knockdown therefore successfully reversed the increase in proliferation induced by BK treatment. Taken together, these results suggested that BK stimulated RCEC proliferation, potentially via the ZO‑1/ZONAB pathway. The signaling paradigm disclosed in the present study potentially serves as an important therapeutic target for cornea regeneration and transplantation.

Novel potential treatment modalities for ocular hypertension: focus on angiotensin and bradykinin system axes

Despite the availability of modern surgical procedures, new drug delivery techniques, health authority-approved single topical ocular drugs, and combination products thereof, there continues to be an unmet medical need for novel treatment modalities for preserving vision. This is especially true for the treatment of glaucoma and the high risk factor often associated with this ocular disease, elevated intraocular pressure (IOP). Undesirable local or systemic side effects, frequency of dosing, lack of sustained IOP lowering, and lack of prevention of diurnal IOP spikes are among the greatest challenges. The very recent discovery, characterization, and publication of 2 novel IOP-lowering agents that pertain to the renin-angiotensin and kallikrein-kinin axes potentially offer novel means to treat and control ocular hypertension (OHT). Here, some contextual introductory information is provided first, followed by more detailed discussion of the properties and actions of diminazene aceturate (DIZE; a novel angiotensin-converting enzyme-2 activator) and FR-190997 (a nonpeptide bradykinin receptor-2 agonist) in relation to their anti-OHT activities in rodent and cynomolgus monkey eyes, respectively. It is anticipated that these compounds will pave the way for future discovery, development, and marketing of novel drugs to treat glaucoma and thus help save sight for millions of people afflicted with this slow progressive optic neuropathy.

Preclinical pharmacology, ocular tolerability and ocular hypotensive efficacy of a novel non-peptide bradykinin mimetic small molecule

We sought to characterize the ocular pharmacology, tolerability and intraocular pressure (IOP)-lowering efficacy of FR-190997, a non-peptidic bradykinin (BK) B2-receptor agonist. FR-190997 possessed a relatively high receptor binding affinity (Ki = 27 nM) and a high in vitro potency (EC50 = 18.3 ± 4.4 nM) for inositol-1-phosphate generation via human cloned B2-receptors expressed in host cells with mimimal activity at B1-receptors. It also mobilized intracellular Ca2+ in isolated human trabecular meshwork (h-TM), ciliary muscle (h-CM), and in immortalized non-pigmented ciliary epithelial (h-iNPE) cells (EC50s = 167-384 nM; Emax = 32-86% of BK-induced response). HOE-140, a selective B2-receptor antagonist, potently blocked the latter effects of FR-190997 (e.g., IC50 = 7.3 ± 0.6 nM in h-CM cells). FR-190997 also stimulated the release of prostaglandins (PGs) from h-TM and h-CM cells (EC50s = 60-84 nM; Emax = 29-44% relative to max. BK-induced effects). FR-190997 (0.3-300 μg t.o.) did not activate cat corneal polymodal nociceptors and did not cause ocular discomfort in Dutch-Belted rabbits, but it was not well tolerated in New Zealand albino rabbits and Hartley guinea pigs. A single topical ocular (t.o.) dose of 1% FR-190997 in Dutch-Belted rabbits and mixed breed cats did not lower IOP. However, FR-190997 efficaciously lowered IOP of conscious ocular hypertensive cynomolgus monkey eyes (e.g., 34.5 ± 7.5% decrease; 6 h post-dose of 30 μg t.o.; n = 8). Thus, FR-190997 is an unexampled efficacious ocular hypotensive B2-receptor non-peptide BK agonist that activates multiple signaling pathways to cause IOP reduction.

FR-190997, a nonpeptide bradykinin B2-receptor partial agonist, is a potent and efficacious intraocular pressure lowering agent in ocular hypertensive cynomolgus monkeys

Preclinical Research FR-190997 (8-[2,6-dichloro-3-[N-[(E)-4-(N-methylcarbamoyl) cinnaminoacetyl]-N-methylamino]benzyloxy]-2-methyl-4- (2-pyridylmethoxy) quinoline), a nonpeptide bradykinin (BK) B2-receptor-selective agonist, represents a novel class of ocular hypotensive agents. FR-190997 exhibited a high affinity for the human cloned B2-receptor (Ki = 9.8 nM) and a relatively high potency (EC50 = 155 nM) for mobilizing intracellular Ca(2+) ([Ca(2+)]i) in human ocular cells from nonpigmented ciliary epithelium; trabecular meshwork [h-TM]; ciliary muscle [h-CM] that are involved in regulating intraocular pressure (IOP). Unlike BK, FR-190997 behaved as a partial agonist (Emax = 38-80%) in these cells and its [Ca(2+)]i-mobilizing effects were blocked by the B2-receptor-selective antagonists (HOE-140, Ki = 0.8-7 nM; WIN-64338, Ki = 157-425 nM). FR-190997 stimulated the production of prostaglandins (PGs) in h-CM and h-TM cells (EC50 = 15-19 nM; Emax = 27-33%); an effect that was reduced by the cyclooxygenase-2 inhibitor bromfenac, and by HOE-140. FR-190997 also induced pro-matrix metalloproteinase (MMP)-1 and MMP-3 release from h-CM cells. FR-190997 significantly lowered IOP (37% [P < 0.001] with 30 μg, 24 h post-topical ocular dosing) in ocular hypertensive eyes of conscious Cynomolgus monkeys. This effect was reduced by bromfenac and completely blocked by a B2-antagonist. FR-190997 primarily stimulated uveoslceral outflow (UVSO) of aqueous humor (2.6 to 3.9-fold above baseline). In conclusion, FR-190997 is a B2-receptor selective partial agonist that activates phospholipase C, mobilizes [Ca(2+)]; induces PG and pro-MMP production, and that profoundly lowers IOP by promoting UVSO in ocular hypertensive Cynomolgus monkey eyes.

Protein expression, biochemical pharmacology of signal transduction, and relation to intraocular pressure modulation by bradykinin B₂ receptors in ciliary muscle

PURPOSE

To examine the bradykinin (BK) B₂-receptor system in human and monkey ciliary muscle (CM) using immunohistochemical techniques, and to pharmacologically characterize the associated biochemical signal transduction systems in human CM (h-CM) cells. BK-induced modulation of intraocular pressure (IOP) in pigmented Dutch-Belt rabbits and cynomolgus monkeys was also studied.

METHODS

Previously published procedures were used throughout these studies.

RESULTS

The human and monkey ciliary bodies expressed high levels of B₂-receptor protein immunoreactivity. Various kinins differentially stimulated [Ca²⁺](i) mobilization in primary h-CM cells (BK EC₅₀=2.4±0.2 nM > Hyp³,β-(2-thienyl)-Ala⁵,Tyr(Me)⁸-(®)-Arg⁹-BK (RMP-7) > Des-Arg⁹-BK EC₅₀=4.2 µM [n=3-6]), and this was blocked by B₂-selective antagonists, HOE-140 (IC₅₀=1.4±0.1 nM) and WIN-63448 (IC₅₀=174 nM). A phospholipase C inhibitor (U73122; 10-30 µM) and ethylene glycol tetraacetic acid (1-2 mM) abolished the BK-induced [Ca²⁺](i) mobilization. Total prostaglandin (primarily PGE₂) secretion stimulated by BK and other kinins in h-CM cells was attenuated by the cyclooxygenase inhibitors bromfenac and flurbiprofen, and by the B₂-antagonists. BK and RMP-7 (100 nM) induced a twofold increase in extracellular signal-regulated kinase-1/2 phosphorylation, and BK (0.1-1 µM; at 24 h) caused a 1.4-3.1-fold increase in promatrix metalloproteinases-1-3 release. Topical ocular BK (100 µg) failed to alter IOP in cynomolgus monkeys. However, intravitreal injection of 50 µg of BK, but not Des-Arg⁹-BK, lowered IOP in rabbit eyes (22.9±7.3% and 37.0±5.6% at 5 h and 8 h post-injection; n=7-10).

CONCLUSIONS

These studies have provided evidence of a functional endogenously expressed B₂-receptor system in the CM that appears to be involved in modulating IOP.

Bradykinin-mediated cell proliferation depends on transactivation of EGF receptor in corneal fibroblasts

In previous studies, bradykinin (BK) has been shown to induce cell proliferation through BK B2 receptor (B2R) via p42/p44 MAPK in Statens Seruminstitut Rabbit Corneal Cells (SIRCs). In addition to this pathway, EGFR transactivation pathway has been implicated in linking a variety of G-protein coupled receptors to MAPK cascades. Here, we further investigate whether these transactivation mechanisms participating in BK-induced cell proliferation in SIRCs. Using an immunofluorescence staining and RT-PCR, we initially characterize that SIRCs were corneal fibroblasts and predominantly expressed B2R by BK. Inhibition of p42/p44 MAPK by the inhibitors of Src, EGFR, and Akt or transfection with respective siRNAs prevents BK-induced DNA synthesis in SIRCs. The mechanisms underlying these responses were mediated through phosphorylation of Src and EGFR via the formation of Src/EGFR complex which was attenuated by PP1 and AG1478. Moreover, BK-induced p42/p44 MAPK and Akt activation was mediated through EGFR transactivation, which was diminished by the inhibitors of MMP-2/9 and heparin-binding EGF-like factor (HB-EGF). Finally, increased nuclear translocation of Akt and p42/p44 MAPK turns on early gene expression leading to cell proliferation. These results suggest that BK-induced cell proliferation is mediated through c-Src-dependent transactivation of EGFR via MMP2/9-dependent pro-HB-EGF shedding linking to activation of Akt and p42/p44 MAPK in corneal fibroblasts.

NPR-B natriuretic peptide receptors in human corneal epithelium: mRNA, immunohistochemistochemical, protein, and biochemical pharmacology studies

PURPOSE

To demonstrate the presence of natriuretic peptide receptors (NPRs) in primary human corneal epithelial cells (p-CEPI), SV40-immortalized CEPI cells (CEPI-17-CL4) and in human corneal epithelium, and to define the pharmacology of natriuretic peptide (NP)-induced cGMP accumulation.

METHODS

NPR presence was shown by RT-PCR, western blot analysis, and indirect immunofluoresence. cGMP accumulation was determined using an enzyme immunoassay.

RESULTS

p-CEPI and CEPI-17-CL4 cells expressed mRNAs for NPR-A and NPR-B. Proteins for both NPRs were present in these cells and in human corneal epithelium. C-type NP (CNP), atrial NP (ANP) and brain NP (BNP) stimulated the accumulation of cGMP in a concentration-dependent manner in p-CEPI cells (potency; EC(50s)): CNP (1-53 amino acids) EC(50)=24+/-5 nM; CNP fragment (32-53 amino acids) EC(50)=51+/-8 nM; ANP (1-28 amino acids) EC(50)=>10 microM; BNP (32 amino acids) EC(50)>10 microM (all n=3-4). While the NPs were generally more potent in the CEPI-17-CL4 cells than in p-CEPI cells (n=4-9; p<0.01), the rank order of potency of the peptides was essentially the same in both cell types. Effects of CNP fragment in p-CEPI and CEPI-17-CL4 cells were potently blocked by HS-142-1, an NPR-B receptor subtype-selective antagonist (K(i)=0.25+/-0.05 microM in CEPI-CL4-17; K(i)=0.44+/-0.09 microM in p-CEPIs; n=6-7) but less so by an NPR-A receptor antagonist, isatin (K(i)=5.3-7.8 microM, n=3-7).

CONCLUSIONS

Our studies showed the presence of NPR-A and NPR-B (mRNAs and protein) in p-CEPI and CEPI-17-CL4 cells and in human corneal epithelial tissue. However, detailed pharmacological studies revealed NPR-B to be the predominant functionally active receptor in both cell-types whose activation leads to the generation of cGMP. While the physiologic role(s) of the NP system in corneal function remains to be delineated, our multidisciplinary findings pave the way for such future investigations.

Biochemical and pharmacological characterization of the human bradykinin subtype 2 receptor produced in mammalian cells using the Semliki Forest virus system

Bradykinin, a vasoactive peptide, plays a crucial role in many cardiovascular processes via activation of the bradykinin subtype 2 receptor (B2R). B2R, a member of the G protein-coupled receptor (GPCR) superfamily, is a potential drug target in the treatment of cardiovascular disorders, pain and inflammation. In this study, human B2R was expressed at high levels in baby hamster kidney (BHK) cells using Semliki Forest virus-based vectors. The recombinant receptor was produced as a fusion protein with affinity tags and an expression level of 11 pmol/mg (i.e., approx. 0.2 mg of active receptor per liter of culture) was obtained. Radioligand binding analysis revealed that the recombinant receptor binds to its endogenous ligand bradykinin with high affinity (Kd = 0.12 nM) and its pharmacological profile was similar to that of B2R in native tissues. Bradykinin-stimulated accumulation of inositol phosphate was observed in BHK cells expressing the recombinant receptor, which indicated the activation of endogenous G alpha(q) protein by the recombinant B2R. Confocal laser scanning microscopy and immunogold staining revealed that the recombinant receptor was predominantly localized intracellularly. To the best of our knowledge, this is the first report of an affinity-tagged recombinant B2R been expressed at high levels in BHK cells and extensively characterized.

Sensory nerves, neurogenic inflammation and pain: missing components of alternative irritation strategies? A review and a potential strategy

The eyes and skin are highly innervated by sensory nerves; stimulation of these nerves by irritants may give rise to neurogenic inflammation, leading to sensory irritation and pain. Few in vitro models of neurogenic inflammation have been described in conjunction with alternative skin and eye irritation methods, despite the fact that the sensory innervation of these organs is well-documented. To date, alternative approaches to the Draize skin and eye irritation tests have proved largely successful at classifying severe irritants, but are generally poor at discriminating between agents with mild to moderate irritant potential. We propose that the development of in vitro models for the prediction of sensory stimulation will assist in the re-classification of the irritant potential of agents that are under-predicted by current in vitro strategies. This review describes the range of xenobiotics known to cause inflammation and pain through the stimulation of sensory nerves, as well as the endogenous mediators and receptor types that are involved. In particular, it focuses on the vanilloid receptor, its activators and its regulation, as these receptors function as integrators of responses to numerous noxious stimuli. Cell culture models and ex vivo preparations that have the potential to serve as predictors of sensory irritation are also described. In addition, as readily available sensory neuron cell line models are few in number, stem cell lines (with the capacity to differentiate into sensory neurons) are explored. Finally, a preliminary strategy to enable assessment of whether incorporation of a sensory component will enhance the predictive power of current in vitro eye and skin testing strategies is proposed.

The application of counter immunoelectrophoresis (CIE) in ocular protein studies

The kinin family are a group of bioactive peptides that are closely involved in the modulation of vascular inflammation and local injury. We have demonstrated here, for the first time, a link between kinin activity and contact lens wear. Protein extracts from daily and extended wear etafilcon A, Group IV, Acuvue lenses (Vistakon), were analysed by counter immunoelectrophoresis. In this way, kinin activity associated with contact lens wear was detected. High molecular weight kininogen was used as the marker protein. In contrast, no kinin activity was detected in the non-lens wearing normal eye.

AL-3138 antagonizes FP prostanoid receptor-mediated inositol phosphates generation: comparison with some purported FP antagonists

The aim of this study was to pharmacologically characterize the antagonist properties of a novel prostaglandin F2alpha (PGF2alpha) analogue (11-deoxy-16-fluoro PGF2alpha; AL-3138) using a variety of second-messenger assays of prostaglandin receptor subtypes. A detailed comparison was made between AL-3138 and some purported FP receptor antagonists such as PGF2alpha dimethylamine, PGF2alpha dimethylamide, glibenclamide and phloretin using the FP receptor-mediated phosphoinositide turnover assay in A7r5 rat thoracic aorta smooth muscle cells and mouse Swiss 3T3 fibroblasts. The potency and efficacy of AL-3138 as an FP receptor agonist were: EC50 = 72.2 +/- 17.9 nM (Emax = 37%) (n = 3) in A7r5 cells and EC50 = 20.5 +/- 2.8 nM (Emax = 33%) (n = 5) in 3T3 cells. Being a partial agonist, the antagonist potency of AL-3138 against fluprostenol in A7r5 cells was determined to be: Ki = 296 +/- 17 nM (n = 3) and Kb = 182 +/- 44 nM (n = 5) (-log Kb = 6.79 +/- 0.1). AL-3138 exhibited very minimal or no antagonistic effects at EP2, EP4, DP and TP prostaglandin receptors. Both PGF2alpha dimethylamide and PGF2alpha dimethylamine were inactive as FP receptor antagonists, whereas phloretin and glibenclamide were very weak and had -log Kb values of 5.28 +/- 0.09 (n = 3) and 3.58 +/- 0.32 (n = 3), respectively. However, phloretin antagonized functional responses of EP2 and DP prostanoid receptors, and also the V1-vasopressin receptor. AL-3138 competed for [3H]PGF2alpha binding to FP receptors with a relatively high affinity (IC50high = 312 +/- 95 nM) matching its functional antagonist potency. In conclusion, AL-3138 is a more potent and selective FP receptor antagonist than glibenclamide, phloretin, PGF2alpha dimethylamide and PGF2alpha dimethylamine and is therefore a unique and novel pharmacological tool to help characterize FP receptor-mediated functions.

Prostaglandin DP receptors positively coupled to adenylyl cyclase in embryonic bovine tracheal (EBTr) cells: pharmacological characterization using agonists and antagonists

Various prostaglandin agonists representing various classes of receptor subtypes were evaluated for their ability to stimulate adenylyl cyclase via the endogenous DP receptor in embryonic bovine tracheal (EBTr) cells. Two antagonists were used to block the agonist-induced cyclic AMP production. ZK118182 (EC50 = 16+/-4 nM), RS-93520 (EC50 = 23+/- 4 nM), SQ27986 (EC50 = 33+/-9 nM), ZK110841 (EC50 = 33+/-5 nM), BW245C (EC50 = 59+/-19 nM) and PGD2 (EC50=101+/-10 nM) (n = 4-70) were the most potent agonists. Whilst most compounds were full agonists (Emax = 100% relative to PGD2), BW245C was significantly more efficacious than PGD2 (Emax = 121+/-3%; P<0.001) and RS-93520 appeared to be a partial agonist (Emax = 64+/-9%; P<0.001). Agonists from the EP (e.g. enprostil; misoprostol; butaprost), FP (e.g. cloprostenol; fluprostenol; PHXA85), IP (iloprost; PGI2) and TP (U46619) prostanoid receptor classes were weak agonists or inactive in the EBTr cell assay system. The DP-receptor antagonist, BWA868C, showed a competitive antagonist profile with pA2 values of 8.00+/-0.02 and 8.14+/-0.13 in Schild analyses with two structurally different agonists, BW245C and ZK118182, respectively (n = 3). AH6809, another purported DP-receptor antagonist, weakly inhibited PGD2- and ZK 18182-induced cyclic AMP production (K(i)s = 808+/-193 nM and 782+/-178 nM, respectively). The current studies have characterized the DP receptor positively coupled to adenylyl cyclase in EBTr cells using a wide range of agonist and antagonist prostaglandins. These data support the utility of the EBTr cell line as a useful tool for the evaluation of DP receptor agonists and antagonists and for profiling other classes of prostaglandins.

Pharmacology of [3H]-pyrilamine binding and of the histamine-induced inositol phosphates generation, intracellular Ca2+ -mobilization and cytokine release from human corneal epithelial cells

We recently reported on the successful generation of immortalized (CEPI-17-CL4) cells from primary human corneal epithelial (P-CEPI) cells which exhibited phenotypic, immunohistochemical and metabolic characteristics akin to the P-CEPI cells. The aims of the present studies were to investigate the ligand binding and functional coupling of the histamine receptors to various biochemical and physiological systems in the P-CEPI and CEPI-17-CL4 cells and to relate these findings to the normal and/or pathophysiological role of histamine on the human ocular surface. Specific [3H]-pyrilamine binding to CEPI-17-CL4 cell homogenates comprised >93% of the total binding and represented interaction with an apparent single population of high affinity (Kd=3.76+/-0.78 nM; n=4) and saturable (Bmax = 1582+/-161 fmol g(-1) tissue) number of histamine-1 (H1) receptor binding sites on CEPI-17-CL4 cell homogenates. The H1-receptor selective antagonists, pyrilamine (Ki=3.6+/-0.84 nM, n=4) and triprolidine (Ki = 7.7+/-2.6 nM, n=3), potently displaced [3H]-pyrilamine binding, while the H2- and H3-receptor selective antagonists, ranitidine and clobenpropit, were weak inhibitors (K(i)s>13 microM). Histamine induced phosphoinositide (PI) hydrolysis 2.7-4.4 fold above basal levels and with a potency of 14.9+/-4.9 microM (n=9) and 4.7+/-0.2 microM (n=9) in P-CEPI and CEPI-17-CL4 cells, respectively. Histamine-induced PI turnover was antagonized by H1-receptor selective antagonist, triprolidine, with a potency (Ki) of 3.2+/-0.66 nM (n=10) and 3.03+/-0.8 nM (n=4) in P-CEPI and CEPI-17-CL4 cells, respectively, but weakly effected by 10 microM cimetidine and clobenpropit, H2- and H3-receptor antagonists. The PI turnover response was attenuated by pre-treatment of the cells with the selective phospholipase C inhibitor, U73122 (1-(6-((17beta-3-methoxyestra- 1,3,5(10)-trien-17-yl)amino)hexyl)-1H-pyrrole-2,5-dione) (IC50=4.8+/-2.4 microM, n = 3). Histamine stimulated intracellular Ca2+ ([Ca2+]i) mobilization in CEPI-17-CL4 cells with a potency of 6.3+/-1.5 microM (n=4). The histamine-induced [Ca2+]i mobilization was reduced by about 28% following pre-incubation of the cells with 4 mM EGTA. While triprolidine completely inhibited histamine-induced [Ca2+]i mobilization, it did not influence the bradykinin-induced [Ca2+]i mobilization response. Histamine (EC50s = 1.28-2.77 microM, n=3-4) concentration-dependently stimulated the release of interleukin-6 (IL-6), IL-8 and granulocyte macrophage colony-stimulating factor, but it did not significantly alter release of tumour necrosis factor-alpha, PGE2 or collagenase-1 (matrix metalloproteinase-1; MMP-1) from CEPI cells. However, IL-1 (10 ng ml(-1)), foetal bovine serum (10%) and phorbol-12-myristate-13-acetate (3 microg ml(-1)) were effective positive control secretagogues of all the cytokines, PGE2 and MMP-1, respectively, from these cells. It is concluded that the CEPI cells express H1-histamine receptors which are positively coupled to PI turnover and [Ca2+]i mobilization which may be directly or indirectly responsible for the release of various cytokines from these cells at physiologically and/or pathologically relevant concentrations.

Effects of bradykinin on signal transduction, cell proliferation, and cytokine, prostaglandin E2 and collagenase-1 release from human corneal epithelial cells

1. We recently demonstrated the presence of phospholipase C-coupled bradykinin (BK) B2-receptors in human primary and SV40 virus-immortalized corneal epithelial (CEPI) cells. 2. The aims of the present studies were to demonstrate the specific binding of [3H]-BK to CEPI cell membranes and to study its pharmacological characteristics. In addition, we wished to study the functional coupling of the BK receptors to various physiological and pathological mechanisms in the CEPI cells, including phosphoinositide (PI) turnover, intracellular Ca2+-mobilization ([Ca2+]i), cell proliferation (via [3H]-thymidine incorporation), and the release of various cytokines, collagenase-1 (matrix metalloproteinase-1) and prostaglandin E2 (PGE2). 3. Specific [3H]-BK binding comprised 83 +/- 2% of the total binding, and was of high affinity (Kd = 1.66 +/- 0.52 nM, n = 5), saturable (Bmax = 640 +/- 154 fmol g(-1) wet weight) and reversible. Competition studies yielded the following affinity values for BK and a number of BK-related peptides: Hoe-140 (D-Arg-[Hyp3,Thi5,D-Tic7,Oic8]BK; icatibant): Ki = 0.17 +/- 0.07 nM; BK: Ki = 1.0 +/- 0.11 nM; [Tyr8]-BK: Ki = 12.9 +/- 2.3 nM; [des-Arg9]-BK: Ki > 9,200 nM (all n = 3-5)). 4. BK potently stimulated PI turnover (EC50 = 2.3 +/- 0.3 nM; n = 7) and [Ca2+]i mobilization (EC50 = 8-20 nM) in CEPI cells and both responses were inhibited in a concentration-dependent manner by 100 nM-10 microM Hoe-140, a selective B2-receptor antagonist, and also inhibited by the selective phospholipase C (PLC) inhibitor, U73122 (1-(6-((17beta-3-methoxyestra-1,3,5(10)-trien-17-yl)amino)hexyl)-1 H-pyrrole-2,5-dione) (IC50 = 3.0 +/- 1.6 microM). BK-induced [Ca2+]i mobilization was reduced by about 30% in the presence of 4 mM EGTA, but was not significantly affected by 100 nM nifedipine. 5. BK (0.1 nM-10 microM) significantly (P<0.05-0.001) stimulated [3H]-thymidine incorporation into CEPI cellular DNA. However, while interleukin-1alpha (IL-1alpha; 10 ng ml(-1)) potently stimulated the release of IL-6, IL-8 and granulocyte macrophage colony-stimulating factor from CEPI cells, BK (0.1 nM-10 microM) was without effect. 6. Whilst phorbol-12-myristate-13-acetate (PMA; 3 microg ml(-1)) and 10% foetal bovine serum (positive control agents) significantly stimulated the release of both MMP-1 and PGE2 from CEPI cells, BK (0.1 nM-10 microM) was without any significant effect under these conditions. 7. In conclusion, these data indicate that the CEPI cells express high-affinity [3H]-BK binding sites representing B2-subtype BK receptors coupled to PI turnover and [Ca2+]i mobilization which appear to stimulate [3H]-thymidine incorporation into cellular DNA. In contrast, BK failed to elicit the release of PGE2, various cytokines and MMP-1 from CEPI cells. These results suggest that BK may have a potential role in corneal epithelium wound healing by stimulating cell proliferation.

Negative cooperativity in the human bradykinin B2 receptor

A human kidney bradykinin (BK) B2 receptor cDNA was transfected in CHO-K1 cells to establish cell lines that express stably and at high density a receptor exhibiting B2 receptor properties in terms of coupling to cell signaling effectors, desensitization, and internalization. A cell line with a density of 1.3 x 10(6) receptors/cell allowed us to carry out a detailed study of BK-receptor interaction over a wide range of BK concentrations. A model assuming that BK binds to two receptor affinity states (depending on guanine nucleotide-sensitive coupling) was not sufficient to account for the kinetics of BK binding. Equilibrium kinetic analysis and studies of the effects of receptor occupancy by agonists or antagonists on the kinetics of BK-receptor complex dissociation revealed features typical of negative cooperative binding. The negative cooperativity phenomenon was also observed in isolated membranes in both the presence and absence of guanine nucleotide. Thus, following the interaction with BK, B2 receptor molecules likely interact with each other, resulting in an acceleration of bound ligand dissociation and a decrease in the apparent affinity of the receptor for BK. This phenomenon can participate in the desensitization process.