Human Ciliary Muscle Cell FP Prostaglandin Receptor Activation By Bimatoprost And Other FP Agonist Prostaglandin Analogues

Abstract

Abstract: : Purpose: The ciliary muscle (CM) plays a critical role in aqueous humor dynamics to regulate intraocular pressure (IOP) in the anterior segment of the eye. The pharmacology of the prostanoid receptor mediating phosphoinositide (PI) hydrolysis, intracellular Ca²⁺ [Ca²⁺]_i mobilization, activation of mitogen–activated protein (MAP) kinase and release of matrix metalloproteinases (MMPs) was studied in cultured human CM (h–CM) cells. Methods: h–CM cells isolated and cultured from eyes of five human donors (ages 33–75 years) were used in these studies. Well documented biochemical and pharmacological procedures were utilized to study the actions of numerous prostaglandins in h–CM cells. Results: Travoprost acid exhibited the highest agonist potency (EC₅₀ = 2.6 ± 0.8 nM) followed by bimatoprost acid (EC₅₀ = 3.6 ± 1.2 nM), PGF_2α (EC₅₀ = 134 ± 17 nM), latanoprost acid (EC₅₀ = 198 ± 83 nM), unoprostone (EC₅₀ = 5.5 ± 1.5 µM) and bimatoprost (EC₅₀ = 9.6 ± 1.1 µM) in the PI turnover assays. A similar rank order of potency was observed for the stimulation of [Ca²⁺]_i mobilization and MAP kinase activation. The FP receptor antagonist, AL–8810, blocked these functional responses. The pharmacological properties of h–CM cell FP receptor correlated well with those of cloned human FP receptors, and also with FP receptors in h–TM, mouse 3T3 cells and rat A7r5 cells (r = 0.9, p < 0.0001). Various prostanoids also stimulated pro–MMP–1 and pro–MMP–2 secretion (EC₅₀ = 3.5 – 4.1 nM) which was blocked by the MAP kinase inhibitor, PD–98059. Conclusions: Functional FP prostaglandin receptors are present on h–CM cells where bimatoprost, unoprostone and free acids of travoprost, latanoprost and bimatoprost exhibit agonist activity as determined by use of multiple assay systems. Furthermore, the potent agonist activity of bimatoprost acid in h–CM cells can explain the IOP–lowering activity of bimatoprost since the latter is readily hydrolyzed to the free acid by ocular tissues upon topical ocular administration.

Keywords: eicosanoids • receptors: pharmacology/physiology • ciliary muscle