Metabolism of arachidonic acid by isolated rabbit ciliary epithelium

A Second Generation Prostanoid Receptor Antagonist Acting at Multiple Receptor Subtypes

It has previously been reported that a prototypical compound (AGN 211377), which blocks pro-inflammatory prostanoid receptors (DP₁, DP₂, EP₁, EP_4, FP, TP) and leaves open IP and EP₂ receptors so that their anti-inflammatory properties could be exerted, produced superior inhibitory effects on cytokine release from human macrophages compared to cyclooxygenase (COX) inhibitors. This favorable activity profile translated into animal studies, with AGN 211377 exceeding the level of inhibition afforded by COX inhibition. AGN 211377 was not, however, a practical drug candidate, having poor bioavailability and cost of goods concerns. Compound 1 (designated AGN 225660) represents a second-generation compound with an entirely different "druggable" core structure. Such a dramatic change in chemical scaffold created uncertainty with respect to matching the effects of AGN 211377. AGN 225660 inhibited RANTES, IL-8, and MCP-1 secretion by at least 50%, from TNFα activated human macrophages. Although AGN 225660 reduced TNFα-evoked MCP-1 release from human monocyte-derived macrophages, it increased LPS-induced MCP-1 secretion (up to 2-fold) from human monocyte-derived dendritic cells. However, AGN 225660 inhibited the release of IL12p 70 and IL-23 from human monocyte-derived dendritic cells stimulated by LPS by more than 70%. This effect of AGN 225660 was reproduced in part by the prototype compound AGN 211377 and a combination of selective DP₁, EP₁, EP₄, FP, and TP antagonists. These findings suggest important effects on T cell skewing and disease modification by this class of therapeutic agents. AGN 225660 exhibited good ocular bioavailability and was active in reducing ocular inflammation associated with phacoemulsification surgery, LPS, and arachidonic acid induced uveitis.

Role of protein kinase C in regulation of Na+- and K +-dependent ATPase activity and pump function in corneal endothelial cells

PURPOSE

Na+- and K+-dependent ATPase (Na,K-ATPase) plays an important role in the pump function of the corneal endothelium. We investigated the possible role of protein kinase C (PKC) in regulation of Na,K-ATPase activity and pump function in corneal endothelial cells.

METHODS

Confluent monolayers of mouse corneal endothelial cells were exposed to phorbol 12,13-dibutyrate (PDBu) to induce activation of PKC. ATPase activity of the cells was evaluated by using ammonium molybdate in spectrophotometric measurement of phosphate released from ATP, with Na,K-ATPase activity being defined as the portion of total ATPase activity sensitive to ouabain. Pump function of the cells was measured with a Ussing chamber, with the pump function attributable to Na,K-ATPase activity being defined as the portion of the total short-circuit current sensitive to ouabain.

RESULTS

PDBu (10(-7) M) increased the Na,K-ATPase activity and pump function of the cultured cells. These effects of PDBu were potentiated by the cyclooxygenase inhibitor indomethacin and the cytochrome P(450) inhibitor resorufin and were blocked by okadaic acid, an inhibitor of protein phosphatases 1 and 2A.

CONCLUSIONS

Our results suggest that PKC bidirectionally regulates Na,K-ATPase activity in mouse corneal endothelial cells: it inhibits Na,K-ATPase activity in a cyclooxygenase- and cytochrome P(450)-dependent manner, whereas it stimulates such activity by activating protein phosphatases 1 or 2A.

Constitutive expression and localization of COX-1 and COX-2 in rabbit iris and ciliary body

Prostaglandins are involved in the regulation of intraocular pressure and the blood-aqueous barrier of the eye, and are used for the treatment of glaucoma. The decrease of the constitutively expressed PG-synthesizing enzyme cyclooxygenase-2 (COX-2) has been demonstrated in the ciliary non-pigmented epithelial layer of patients with primary open angle glaucoma. Little is known about the distribution of COX-1 and COX-2 in animals. We investigated this in the iris and ciliary body of the normal rabbit eye. The presence of COX-1 and COX-2 in freshly excised iris and ciliary body tissue from adult New Zealand White albino rabbits was demonstrated by real-time RT-PCR, and Western blot analysis. The localization of both isoforms and of the neuron-specific protein gene product 9.5 was determined by indirect immunofluorescence. Both enzymes are expressed in the iris and the ciliary body. Immunofluorescence studies including double staining techniques localized COX-1 and COX-2 to about 50% of cells in the stromal tissue of iris and ciliary body, mainly on the corneal side. They were co-localized in about 75% of these cells. Whereas all stained cells were positive for COX-1, COX-2 showed a gradient-like distribution in the stroma, with some restriction of expression near the epithelial layers, which we clearly showed to be completely negative for both COX-1 and COX-2. Also, neuronal elements did not show COX-1 or COX-2 immunoreactivity. These results establish the presence of COX-1 and COX-2 on the RNA and protein levels in normal, unstimulated rabbit iris and ciliary body. The pattern of distribution suggests a role for both enzymes in maintaining the physiology of the eye. In contrast to our results in man, non-pigmented epithelial cells of the ciliary body did not express immunoreactivity. This could account for differences in the regulation of intraocular pressure and/or blood-aqueous barrier between human and rabbit eyes.

Prostaglandin E2 binding site distribution and subtype classification in the rabbit iris-ciliary body

The distribution and characteristics of specific binding sites for tritium labeled prostaglandin E2 (3H-PGE2) were examined in membrane preparations from rabbit iris-sphincter, iris and ciliary body. The majority of 3H-PGE2 specific binding sites were found in the ciliary body (46%) followed by the iris (37%) and the iris-sphincter muscle (5%). Scatchard analysis of saturable 3H-PGE2 binding sites in the ciliary body indicated a single binding site with a Kd of 2.81 nM and Bmax value of 84 fmoles bound/mg protein. Competition by agonists selective for the EP1, EP2 and EP3 receptor subtypes of the EP (PGE2) prostanoid receptor indicated that the majority of rabbit ciliary body 3H-PGE2 binding sites are of the EP2 subtype. Incomplete displacement of labeled 3H-PGE2 from its binding sites by the EP2 selective agonist 11-deoxy PGE1 suggests the presence of additional EP or non-EP binding sites. There was essentially no binding to EP1 receptor sites as defined by the displacement of 3H-PGE2 by 17-phenyl-trinor PGE2. A weak displacement of 3H-PGE2 by the EP3/EP1 specific agonist, sulprostone, may account for the presence of a small number of EP3 specific binding sites in this tissue. The predominant distribution of PGE2 binding sites in the ciliary body and their identification as EP2 selective, supports recent functional studies where topical application of prostanoids with EP2 but not EP1 or EP3 agonist activity resulted in breakdown of the blood-aqueous barrier.