Inhibition of increased permeability of the blood-aqueous barrier by non-steroidal anti-inflammatory compounds as demonstrated by fluorescein angiography

EP4 receptor as a novel promising therapeutic target in colon cancer

The most prevalent malignancy that can occur in the gastrointestinal tract is colon cancer. The current treatment options for colon cancer patients include chemotherapy, surgery, radiotherapy, immunotherapy, and targeted therapy. Although the chance of curing the disease in the early stages is high, there is no cure for almost all patients with advanced and metastatic disease. It has been found that over-activation of cyclooxygenase 2 (COX-2), followed by the production of prostaglandin E2 (PGE2) in patients with colon cancer are significantly increased. The tumorigenic function of COX-2 is mainly due to its role in the production of PGE2. PGE2, as a main generated prostanoid, has an essential role in growth and survival of colon cancer cell's. PGE2 exerts various effects in colon cancer cells including enhanced expansion, angiogenesis, survival, invasion, and migration. The signaling of PGE2 via the EP4 receptor has been shown to induce colon tumorigenesis. Moreover, the expression levels of the EP4 receptor significantly affect tumor growth and development. Overexpression of EP4 by various mechanisms increases survival and tumor vasculature in colon cancer cells. It seems that the pathway starting with COX2, continuing with PGE2, and ending with EP4 can promote the spread and growth of colon cancer. Therefore, targeting the COX-2/PGE2/EP4 axis can be considered as a worthy therapeutic approach to treat colon cancer. In this review, we have examined the role and different mechanisms that the EP4 receptor is involved in the development of colon cancer.

Ocular inflammatory responses in the EP2 and EP4 receptor knockout mice

PURPOSE

To examine the role of EP2 and EP4 receptors in murine ocular inflammation.

METHODS

Prostaglandin EP2 and EP4 receptor knockout and wild-type mice were treated topically with prostaglandin E2, SDF-1, and RANTES and lipopolysaccharide by intravitreal injection. Paracentesis was performed by puncturing the cornea. The increase in the level of aqueous humor protein and the number of leukocytes were measured and the vascular leakage of protein was visualized using fluorescein angiography.

RESULTS

In the EP2 receptor knockout mice, there was significant inhibition of the disruption of the blood-aqueous barrier caused by lipopolysaccharides, paracentesis, prostaglandin E2, SDF-1, and RANTES. Reductions in the disruption in the blood-aqueous barrier and leukocyte infiltration after lipopolysaccharide injection and paracentesis were significant, but there was no increase in the aqueous humor protein level after prostaglandin E2 treatment in EP4 receptor knockout mice.

CONCLUSIONS

The results of the present experiments suggest that EP2 and EP4 receptors partly mediate the disruption of the blood-aqueous barrier and leukocyte infiltration induced by prostaglandin E2, SDF-1, RANTES, and lipopolysaccharides.

Prostaglandin E2 receptor subtypes, EP1, EP2, EP3 and EP4 in human and mouse ocular tissues--a comparative immunohistochemical study

The purpose of the present study was to compare the localization of prostaglandin E(2) receptor subtypes in normal human and mouse ocular tissues. Paraffin embedded sections of normal human and mouse (129 Sv/Ev) eyes were treated with EP(1), EP(2), EP(3) and EP(4) specific antibodies and subsequently incubated with Alexa Fluor secondary antibody (Ex/Em=555/571) to detect the presence of EP receptor proteins. Fluorescence of the localized antibodies was visualized in a Carl Zeiss Microscope (Axiovert 200) and photographed using Carl Zeiss Axiocam camera. In mice EP(1) and EP(3) receptor subtypes were only moderately expressed, EP(3) receptor expression being almost negligible. In human cornea and iris ciliary body, EP(1) and EP(3) receptors were prominently expressed. EP(4) receptor was expressed moderately in human and mouse ocular tissues. EP(2) receptor was the most prominently and abundantly expressed receptor in both human and mouse ocular tissues. It is concluded that the pattern of the distribution of EP receptor subtypes in the ocular tissues are similar in human and mouse. Thus, 129 Sv/Ev strains of mice would make an appropriate animal model for studying the ocular pathophysiological roles of prostaglandin receptor agonists.

Blood-aqueous barrier in prostaglandin EP2 receptor knockout mice

The role of prostaglandin EP(2) receptors in the disruption of the blood-aqueous barrier was examined using EP(2) receptor-deficient mice. Eyes were topically treated with EP receptor agonists or subjected to paracentesis. Fluorescein angiography was performed after topical treatment with 2.0 icrog butaprost. The results show that EP receptor agonists, PGE( 2) and the EP(2) receptor-selective agonist butaprost, increased aqueous humor protein in EP(2) +/+ wild-type mice to 18.0 mg/ml and 12.0 mg/ml, respectively, from the control value of 2.7 mg/ml. The increase in aqueous humor protein concentration in response to these EP receptor agonists was reduced significantly in EP(2) receptor-deficient mice. Fluorescein leakage into the anterior chamber, two minutes after its injection, was significantly greater in butaprost-treated wild-type mice than in butaprost-treated knockout mice. Protein concentration, 15 min after paracentesis, increased from 2.2 mg/ml to 25.0 mg/ml in the aqueous humor of the eyes of wild-type mice, while the increase in knockout mice was 10.6 mg/ml. These results suggest that EP( 2) and EP(4) receptors mediate the disruption of the blood-aqueous barrier induced by EP receptor agonists and paracentesis.

Pharmacokinetics of fluconazole in cerebrospinal fluid and serum of rabbits: validation of an animal model used to measure drug concentrations in cerebrospinal fluid

Complete concentration-time data describing the pharmacokinetics of fluconazole in the cerebrospinal fluid (CSF) following a single dose are not available for humans or animals. We studied the pharmacokinetics of fluconazole with an indwelling intracisternal needle as described by R.G. Dacey and M.A. Sande (Antimicrob. Agents Chemother. 6:437-441, 1974). To determine whether the presence of an intracisternal needle alters pharmacokinetics in the CSF, we validated this model with uninfected rabbits by measuring pharmacokinetic constants following direct intracisternal and intravenous administration of fluconazole. Following direct injection, there was no alteration of elimination rates in the CSF with increasing sample number or time. Following intravenous administration, the penetration and kinetic constants were the same in individual animals from which multiple CSF samples were obtained as in a composite subject constructed by pooling virgin samples from different animals. The presence of the intracisternal needle did not alter CSF chemistry or leukocyte counts, and erythrocyte contamination was < 0.001%. While drug concentrations were measured by a microbiological assay, we also compared the sensitivity and reproducibility of a high-performance liquid chromatography (HPLC) assay with those of the microbiological assay. Following a single intravenous dose, the maximum concentration of the drug in serum, the time to maximum concentration of the drug in serum, the terminal elimination half-life in the CSF, and the percent penetration by fluconazole were 6.12 micrograms/ml, 1 h, 9.0 h, and 84.3%, respectively. We conclude that the sampling of CSF via an indwelling needle does not alter fluconazole pharmacokinetics, cause inflammation, or alter chemical parameters; that the microbiological assay is at least equivalent in sensitivity and reproducibility to the HPLC assay; and that robust parameters describing the pharmacokinetics of fluconazole are possible with this model.

Review: mediation of the ocular response to injury

The structure of the anterior segment of the eye provide aqueous humour for metabolic traffic, regulation of intraocular pressure and the maintenance of a functional permeability barrier to separate internal compartments from general systemic influences. Irritative and injurous insults to the eye elicit an acute defensive miotic and vascular response which upsets the aqueous dynamics and provokes the influx of blood plasma proteins into the aqueous chambers. These events are initiated by antidromic activation of sensory elements within the anterior segment, releasing substance P and calcitonin gene-related peptide (CGRP) which, in lower mammals at least, stimulate respectively the miotic and vascular reactions. Considerable species differences can be found in the responsiveness of the eye to injury and in the effects of exogenous CGRP and substance P.

Recent experimental studies on the blood-aqueous barrier: the anatomical basis of the response to injury

In the mammalian eye the tissue layers which effectively separate the neural retina and the transparent refractive media from the circulating blood are generally known as the blood-retinal barrier (BRB) and blood aqueous barrier (BAB) respectively. These have been delineated by morphologically identifying the ultrastructural features which impede the passage of molecules from the blood to the working parts of the eye; physiologically, there is a certain amount of overlap in their function, as there is free diffusion of solutes between the aqueous humour, the vitreous humour and the interstitial tissue of the neural retina. Notwithstanding, it is convenient and appropriate to maintain the distinction as the more recent work has focused on the fine structural aspects of these barrier systems. The abundant literature which describes the work leading to the identification and characterisation of these barriers has been reviewed in depth with great authority by several eminent researchers, notably the late Giuseppina Raviola, and Jose Cunha-Vaz. Certain pathological conditions, trauma--including surgical manipulation, and chemical irritation of the eye can cause significant disruption of these barriers with important clinical consequences. In our laboratory interest has centred around vascular and epithelial changes which occur when the eye is injured and which can lead to a breakdown of the BAB. More recently attention has been drawn to functional and behavioural differences between species, particularly with regard to the relative stability of the barrier.

Comparison of the effects of corticosteroids and indomethacin on the response of the blood-aqueous barrier to injury

Aqueous protein content was estimated as a measure of the integrity of the blood-aqueous barrier after paracentesis or argon laser photo-coagulation of the iris in rabbits. Corticosteroid pretreatment topically or by subconjunctival or intramuscular injection exerted only a moderate inhibitory effect on the breakdown of the blood-aqueous barrier. Instillation of 0.1% indomethacin however, strongly inhibited the response in both models. The results are indicative of the potential usefulness of topical administration of prostaglandin synthetase inhibitors in the treatment of non-infectious inflammatory diseases.

Prostaglandin involvement in the responses of the rabbit eye to water-soluble marihuana-derived material

Both anticoagulants (heparin and streptokinase) and non-steroidal anti-inflammatory compounds (aspirin and indomethacin) were used against a water-soluble derivative of marihuana, MDM. While the anticoagulants had no effect on the ocular effects of MDM, both aspirin and indomethacin altered the time course and effected the MDM-induced reduction of intraocular pressure. The usual initial hypertensive effect of intravenous MDM was eliminated and the later intraocular pressure fall occurred earlier as well as being inhibited by about 35 to 50%. Assay for prostaglandins revealed that intravenous MDM (3.86 micrograms) caused a marked rise in PGE2 concentration of the aqueous humor and iris-ciliary body during the first hour or two after administration of MDM, but normal values occurred at 4, 6, and 8 hours when the intraocular pressure is reduced by up to 60%. Following intravitreal MDM (0.002 microgram), however, the PGE2 levels remained unchanged over 24 hours, despite the induction of a fall in intraocular pressure between 14 and 18 hours which lasts for many hours. Prostaglandin appears to be involved in the hypertensive phase of intraocular pressure change after intravenous MDM injection; and, while the fall in intraocular pressure may contain a component partially mediated by prostaglandins, there is no evidence that intravitreal MDM induces any effect on prostaglandin levels. The involvement of prostaglandins, therefore, in the mediation of MDM-induced ocular hypotensive effects is apparently small.

The effect of naproxen on the ocular inflammatory response following extracapsular lens extraction in rabbits

Naproxen effects on the ocular inflammatory response following extracapsular lens extraction were studied in rabbits. Twelve hours before surgery, rabbits were given 20 mg of a 5 mg/ml naproxen suspension by gavage. A maintenance dose of 10 mg naproxen 3 times per day was started on the day of lensectomy and continued throughout the entire observation period. Phakic and aphakic control rabbits received no drug suspension. Central corneal thickness and intraocular pressure measurements were determined pre-operatively, at 4 and 24 h post-operatively and every 24 h thereafter. Four groups of rabbits, sacrificed at 24, 48, 72, and 168 h after lensectomy, had anterior chamber paracentesis performed for PMN (polymorphonuclear leucocyte) counts and determination of protein content. A 5th group had both paracentesis and iris-ciliary body excision for PGE2 assay at 24 h. No parameter was significantly altered by the naproxen regimen compared to untreated rabbits.

Anti-inflammatory effects of ketoprofen in rabbit corneal epithelial wound model

Ocular anti-inflammatory effects of ketoprofen were assessed and compared with indomethacin in the rabbit corneal epithelial wound model. Intraperitoneally (5 mg kg-1 and 50 mg kg-1) and topically (0.01%) administered ketoprofen and topical indomethacin (0.5%) prevented the release of polymorphonuclear leukocytes (PMNs) into the tear fluid of rabbits following partial de-epithelialization. However, 0.001% ketoprofen applied topically potentiated the PMN response. Topical ketoprofen at all doses tested equally inhibited prostaglandin (PG) synthesis in both conjunctiva and iris-ciliary body. In contrast, indomethacin was more effective in inhibiting PG synthesis in conjunctiva than in the iris-ciliary body. In addition, anti-inflammatory doses of ketoprofen did not interfere with wound healing after complete corneal de-epithelialization in rabbits.

Fluorophotometric study of anterior segment barrier functions after extracapsular cataract extraction and posterior chamber intraocular lens implantation

We used fluorophotometry and pachymetry to examine the longer-term (more than three months) postoperative effects in the anterior segment of extracapsular lens extraction with and without posterior chamber intraocular lens implantation. Fluorophotometry was performed after oral administration of fluorescein solution (5 mg/kg of body weight under fasting condition). We calculated the corneal endothelial transfer coefficient, fluorescein distribution ratio, aqueous transfer coefficient in reference to chamber volume, and loss coefficient and measured corneal thickness with a modified pachymeter. There were no significant differences between the values for corneal endothelial transfer coefficient and corneal thickness in the two groups of surgically treated eyes combined vs the intact fellow eyes. The aqueous transfer coefficient and loss coefficient values were not significantly different between the two surgically treated groups. Anterior chamber depth did not differ significantly between the two surgical groups, but the value for the two groups combined (3.79 mm) did differ significantly from that of the fellow eyes (2.87 mm) (P less than .005). We concluded that endothelial function recovers three months after extracapsular lens extraction with or without posterior chamber intraocular lens implantation, and that the effects of intraocular lens implantation on anterior segment barrier functions are not significantly different from those of extracapsular lens extraction alone.

The effect of acetyl-salicylic-acid pretreatment on re-formed aqueous humor. A study of intracapsular lens extraction in the human eye

Aqueous humor (a.h.) was sampled in 67 patients operated on for cataract by intracapsular lens extraction at the start and finish of surgery. Twenty eight of these patients received pretreatment with acetyl-salicylic acid (ASA), to a total of 2.5 g, beginning 18 hours prior to surgery. A serum sample was drawn immediately following the operation from 55 patients. Using radial immunodiffusion, albumin and IgG were measured in primary and secondary a.h. and in serum. The group pretreated with ASA showed a significantly smaller relative increase of IgG (P < 0.05). The increase of the proteins, however, showed no dependence on their serum-level and the only side-effect of the treatment was an unexplained rise in serum-albumin. The possible clinical application of patients with a high risk of postoperative complications is briefly summarized.