The effect of disodium cromoglycate on the release of histamine and degranulation of rat mast cells induced by compound $\text{48}\text{80}$

Mast cells play a critical role in type 1 hypersensitivity reactions. Indeed, mast cell mediators are implicated in many different conditions including allergic rhinitis, conjunctivitis, asthma, psoriasis, mastocytosis and the progression of many different cancers. Thus, there is intense interest in the development of agents which prevent mast cell mediator release or which inhibit the actions of such mediators once released into the environment of the cell. Much progress into the design of new agents has been made since the initial discovery of the mast cell stabilising properties of khellin from Ammi visnaga and the clinical approval of cromolyn sodium. This review critically examines the progress that has been made in the intervening years from the design of new agents that target a specific signalling event in the mast cell degranulation pathway to those agents which have been developed where the precise mechanism of action remains elusive. Particular emphasis is also placed on clinically used drugs for other indications that stabilise mast cells and how this additional action may be harnessed for their clinical use in disease processes where mast cells are implicated.

Successive petroleum ether, chloroform, methanol and water extracts of Bacopa monnieri were tested (in vitro) for mast cell stabilising effect. The methanolic fraction exhibited potent activity comparable to disodium cromoglycate, a known mast cell stabiliser.

The concept of mast cell heterogeneity is well established. Recent data indicate that human conjunctival tissue mast cells and human connective tissue mast cells respond to various secretagogues in similar fashion. It is now recognized that different mast cell populations respond differently to anti-allergic drugs.

The purpose of the study is to compare the effects of three new ocular anti-allergic drugs (nedocromil, olopatadine, and pemirolast) on mediator release from the target human conjunctival mast cell population with those of cromolyn sodium. The affinity of the compounds for the histamine H₁ receptor was also compared.

A monodispersed suspension of partially purified human conjunctival mast cells was prepared from cadaver conjunctival tissue. Mast cells (5 × 10³) were challenged with anti-human IgE in the presence or absence of test drugs, and histamine content of the cell supernatants was determined using a specific radioimmunoassay. H₁ receptor binding activity was assessed using a radioligand binding assay.

Cromolyn and pemirolast (100 nM to 1 mM) failed to significantly inhibit histamine release from human conjunctival mast cells using exposure times of 1 and 15 minutes prior to challenge. Using identical nedocromil concentrations and exposure times, statistically significant (P < .05) inhibition (28%) of histamine release was observed at only the 100 micromolar concentration and 1-minute exposure time. In contrast, olopatadine inhibited histamine release in a concentration-dependent fashion (r = 0.891, n = 59, IC₅₀ = 653 micromolar). Only olopatadine exhibited significant H₁ receptor binding activity at relevant concentrations (K_i = 36 nanomolar, n = 13).

These data indicate that olopatadine possesses anti-allergic activity in the appropriate targets for topical ocular anti-allergic drug therapy, human conjunctival mast cells. Coupled with the compound's antihistaminic activity, this suggests that olopatadine will have efficacy advantages in allergic conjunctivitis patients over the other drugs tested.

Mast cells (MC) can be stimulated to secrete by cross-linking immunoglobulin E bound to specific surface receptors, as well as in response to polycationic molecules such as substance P and compound $\text{48}\text{80}$. The antiallergic drug disodium cromoglycate (cromolyn) inhibited MC secretion and rapidly incorporated phosphate into a 78 kDa protein, speculated to be its mode of action. This protein was purified by single and two-dimensional gel electrophoresis, and was shown to be phosphorylated primarily on serine residues by protein kinase C. Partial amino acid sequencing of two generated fragments was identical to that of portions of mouse moesin, a member of the band 4.1 superfamily of proteins, with no definitive function known to date. Polyclonal antibodies raised against the rat basophil leukemia cell moesin cDNA expressed in Escherichia coli immunoprecipitated the 78 kDa phosphoprotein quantitatively, and immunocytochemistry localized it to the plasma membrane. Reversible phosphorylation of this 78 kDa phosphoprotein could affect its possible cytoskeletal binding through which it may regulate stimulus-secretion coupling in MC.

Gastric mucosal blood flow (GMBF) was measured in the ex vivo stomachs of anesthetized rats simultaneously with mean arterial blood pressure (MBP), luminal pH and transmucosal potential difference (PD) in an attempt to characterize these responses induced by capsaicin. The stomach was mounted on a Lucite chamber, perfused with saline at the flow rate of 1 ml/min, and GMBF was measured by Laser flowmetry. Under these conditions, the pH, PD and GMBF were 3.5 to 4.0, —30 to —35 mV and 8-12 ml/min/100 g, respectively. Mucosal application of capsaicin (0.03-1mg/ml for 10 min) increased GMBF in a concentration-dependent manner, without any change in PD, pH and MBP. The increased GMBF response caused by capsaicin was abolished by chemical deafferentation following systemic capsaicin injections (total dose: 100mg/kg), significantly attenuated by pretreatment with indomethacin (5 mg/kg, s.c.) or ruthenium red (300 μg/kg, i.v.), but was not affected by spantide (100 μ g/kg, i.v.), atropine (300 μg/kg, i.p.) or disodium cromoglycate (30 mg/kg, i.p.). In addition, when the mucosa was exposed to capsaicin repeatedly, this response showed a marked tachyphylaxis at a high concentration (6 mg/ml). These results suggest that intragastric capsaicin increased GMBF selectively through capsaicin-sensitive sensory neurons, and this action may involve endogenous prostaglandins.

Epirubicin induces an important noncytotoxic release of histamine from rat peritoneal cells in vitro. This exocytotic response is inhibited by sodium cromoglycate, similarly to that elicited by the classic mast cell secretagogue, compound 48/80.

Mast cells obtained from the peritoneal cavities of rats treated with epirubicin in vivo were extensively degranulated; in contrast, samples obtained from rats pretreated with sodium cromoglycate showed normal appearing mast cells.

When injected i.p., immediately before the antineoplastic agent, cromolyn significantly improved the survival time and the microscopic appearance of myocardial tissues of epirubicin-treated mice.

The results indicate that histamine release could play an important role in the pathogenesis of anthracycline-induced cardiotoxicity.