Journal of ocular pharmacology最新文献

An implantable sustained release device has been developed to treat chronic disorders of the eye. The device, consisting of a central core of drug encased in layers of permeable and impermeable polymers, can be implanted subconjunctivally or intravitreally. This technique was used to develop a ganciclovir device which, when implanted into the vitreous, maintains therapeutic vitreous levels of drug for 8 months. Initial studies in patients with cytomegalovirus (CMV) retinitis indicate that this treatment may offer better control of the disease and fewer side effects than existing therapies. Cyclosporine A devices were prepared for the treatment of uveitis. Early data suggests that these devices maintain therapeutic levels in the vitreous for approximately 3 years. Work on efficacy and toxicity is continuing. Although clinical applications of these devices are likely to be restricted to diseases requiring chronic drug therapy, they can be used to investigate optimal delivery rates. Subconjunctivally implanted devices releasing 5-FU for 12 days maintained filters in cynomolgus monkeys for 3 months. Similar devices maintained low intraocular pressure in 75% of high risk filter patients.

One of the mainstays of glaucoma treatment is the use of drugs that decrease the secretion of aqueous humor fluid from the ciliary epithelium. Unfortunately, many currently available drugs that decrease aqueous humor production such as beta-adrenergic antagonists, may cause serious systemic side effects such as cardiac arrhythmias and arrest, pulmonary dysfunction, and CNS side effects such as decreased libido and depression. Efforts to develop effective aqueous suppressants that offer decreased morbidity and mortality in comparison to those currently available will likely rely on the ability to alter the function of specific cellular events which underlie aqueous humor production by the ciliary epithelium. However, the secretory process which results in aqueous humor production is incompletely understood and the identification of precise cellular mechanisms which underlie this process remain to be established. We will present a rationale for genetic approaches to regulate gene expression so that aqueous humor production may be specifically targeted in glaucoma patients. Techniques of gene transfer including homologous exchange recombination, and expression of antisense genes, will be discussed.

The occurrence of cholinesterases has been demonstrated in retinas of several mammalian species. Histochemical staining techniques indicate that the acetylcholinesterases (AChE) are present in amacrine cells and their neighboring bipolar cells. However, the nature of retinal cholinesterases and their interactions with specific cholinesterase inhibitors are not known. Therefore, we have studied the inhibition of the rat retinal cholinesterase activity by BW284C51, a selective inhibitor of AChE, and iso-OMPA, a selective inhibitor of butyrylcholinesterase (BChE). Retinas from Zivic-Miller rats were solubilized by sonication in phosphate buffer (0.134 M, pH 7.2) at 4 degrees C for 20 min. The cholinesterase activity in the sonicate was determined by a radiometric method using 14C-acetylcholine (ACh) as substrate (10(-2) M). Excess 14C-ACh was adsorbed by Amberlite CG-120 cation exchange resin. 14C-acetate formed and retained in the aqueous medium was determined by liquid scintillation counting. This study gave the following results: (a) Rat retinal sonicate gave total cholinesterase activity of 3.76 mumol of ACh hydrolyzed/mg protein/15 min; (b) This activity was inhibited by BW284C51 (IC50, 0.115 microM). Iso-OMPA (IC50, 500 microM) did not cause significant inhibition at 0.115 microM. These observations suggest that the rat retinal cholinesterase is predominantly AChE.

Choline acetyltransferase catalyzes the synthesis of acetylcholine from choline and acetylcoenzyme A (ACoA) in both nervous and non-nervous tissues. Carnitine acetyltransferase occurs in several tissues and transfers acetyl groups from ACoA to carnitine forming acetylcarnitine and exhibits weak choline acetyltransferase activity. Several haloacetylcholines and haloacetylcarnitines were synthesized to develop selective inhibitors of choline acetyltransferase and carnitine acetyltransferase. Acetylcholine is a transmitter for some presynaptic neurons and/or amacrine cells in retina. Selective inhibitors of choline acetyltransferase and carnitine acetyltransferase were used in the evaluation of choline acetyltransferase and carnitine acetyltransferase activities in the rat retina. Choline acetyltransferase and carnitine acetyltransferase activities were assayed by transferring of [14C]acetyl group from [14C]ACoA to choline or carnitine and estimating [14C]-acetylcholine or [14C]acetylcarnitine. This study gave the following results: (a) Bromoacetylcholine (BrACh) was a selective inhibitor of purified choline acetyltransferase (I50, 2.2 microM); (b) (R)-bromoacetylcarnitine [(R)-BrACa] was more potent for inhibiting purified carnitine acetyltransferase (I50, 4 microM) than purified choline acetyltransferase (I50, 46 microM); (c) Rat retinal sonicate gave choline acetyltransferase activity of 98 +/- 6 nmol of ACh formed/mg/10 min. When the carnitine acetyltransferase was completely inhibited by (R)-BrACa, the activity for choline acetyltransferase decreased to 47 +/- 1 nmol, and this decrease was possibly due to the formation of some [14C]acetylcholine by carnitine acetyltransferase. The net retinal choline acetyltransferase activity was 51 nmol acetylcholine/mg protein/10 min; (d) Rat retinal sonicate contained carnitine acetyltransferase activity of 102 +/- 7 nmol acetylcarnitine formed/mg protein/10 min. This was not altered by inhibition of choline acetyltransferase with BrACh. This means that choline acetyltransferase did not use carnitine as a substrate. Choline acetyltransferase and carnitine acetyltransferase activities did not change after dialysis of retinal sonicates at 4 degrees C for 24 hrs. These observations suggest that BrACh and (R)-BrACa are useful for assessing the correct values for choline acetyltransferase and carnitine acetyltransferase activities in retinal tissues.

Vascularization of the cornea occurs in many pathological conditions and can result in loss of visual acuity. It is also thought that vascularization predisposes the cornea to reject grafts by facilitating the detection of foreign antigens in donor material. A rat corneal assay for angiogenesis was adopted in the present study to evaluate the possible angiostatic activity of a low molecular weight heparan sulphate (LMW-HS). Corneal lesions were induced by chemical cauterization at 2 mm from the corneoscleral limbus. Rats were randomized to receive two drops/eye four times daily, for 6 days, of a solution of LMW-HS in vehicle (2.5% carboxymethylcellulose), heparin, heparin plus hydrocortisone, or vehicle alone. After a 6 day-treatment period, the eyes were perfused with india ink and the degree of neovascularization was evaluated. In rats treated with vehicle alone a dense vascular network extending from the corneoscleral limbus to the cauterized site was observed; on the contrary, a markedly reduced vascular network was evidenced in animals treated with LMW-HS. The distribution of basic fibroblast growth factor (bFGF) in the cauterized cornea was also evaluated by using an immunohistochemical method. A marked bFGF immunoreactivity was demonstrated in corneal epithelium and stroma of control rats 12-48 hours after the cautery. These results lead to the assumption that LMW-HS could be used in ophthalmology to inhibit corneal neovascularization.

Beta-adrenergic binding sites in primary cultures of chick lens annular pad (CLAP) cells were characterized with dihydroalprenolol (DHAP). Binding site affinities and densities were similar to beta-adrenergic receptors (BARs) previously characterized on crude membranes from freshly isolated cells. In competitive displacement studies, the beta-blocker propranolol was shown to increase the number of available binding sites in a concentration dependent manner. Acute exposure of CLAP cells to propranolol prior to DHAP binding also resulted in an increase in the number of available binding sites. Finally, lens beta-adrenergic binding site levels could be modulated by dexamethasone treatment. These results indicate that lens BARs are subject to common regulatory mechanisms and further implicate ophthalmic pharmaceuticals as possible cataractogenic agents.

We studied the plasma levels and systemic anticholinergic activity of tropicamide after ocular administration in eight women. Two 40 microliters drops of 0.5% tropicamide were instilled into the lower cul-de-sac of one eye of the subjects and concentrations and respective muscarinic receptor occupancy of tropicamide in plasma were monitored using radioligand binding techniques. Tropicamide was rapidly absorbed systemically with the mean peak concentration in plasma being 2.8 +/- 1.7 ng/ml (mean +/- SD) at five minutes after instillation. Tropicamide disappeared rapidly from the systemic circulation: drug concentration in plasma was 0.46 +/- 0.51 ng/ml (mean +/- SD) at 60 minutes and below 240 pg/ml at 120 minutes after instillation. Tropicamide bound to muscarinic receptors of rat brain with an apparent equilibrium binding constant (Ki-value in plasma) 220 +/- 25 nM (mean +/- SD, n = 3). Tropicamide occupied maximally 8% of muscarinic receptors in plasma after ocular application. The low affinity of tropicamide for muscarinic receptors and its negligible receptor occupancy in plasma can explain the low incidence of systemic side-effects of tropicamide eyedrops.

Purpose: Pharmacological modulation of wound healing after glaucoma filtration surgery is of great clinical interest, but there are only limited data available on drug pharmacokinetics following glaucoma filtration surgery. Therefore we have studied the in vivo release and tissue distribution of etoposide (VP-16) delivered subconjunctivally by a bioerodible drug-carrier during filtration surgery in rabbits.

Methods: Disks composed of the polyanhydride 1,3-bis(p-carboxyphenoxy) propane and sebacic acid (PCPP:SA) in a weight ratio of 25:75 and containing 1 mg of 3H-etoposide were placed subconjunctivally during posterior lip sclerectomy in one eye of albino rabbits. Animals were euthanized at various times after surgery and etoposide concentrations in fluids and tissues were determined using liquid scintillation counting.

Results: Release of etoposide from the implant was nearly linear over time, at 30 ug/day, except for a burst between days 6 and 7. By the twelfth postoperative day, 92% of the etoposide had been released. Steady state levels averaged 89 ng/mg in the conjunctiva and sclera, 195 ng/ml in the vitreous, and 29 ng/ml in serum. Drug levels in the aqueous humor, other ocular tissues, and in the contralateral eye were negligible.

Conclusions: The concentration of etoposide delivered by a polyanhydride controlled release device on the ocular surface is sufficient to reduce fibroblast proliferation for at least 12 days after filtration surgery.

Microparticulates are drug-containing small polymeric particles (erodible, non-erodible or ion-exchange resins) that are suspended in a liquid carrier medium. Upon administration of particle suspension in the eye, the particles reside at the delivery site (cul-de-sac, sub conjunctiva or vitreous cavity) and the drug is released from the particles through diffusion, chemical reaction, polymer degradation, or ion-exchange mechanism. Several distinct approaches have been used to formulate drugs in microparticulate dosage form for intraocular and topical application. These include erodible microparticulates, swelling mucoadhesive particulates, pH responsive microparticulates, nanoparticles/latex systems, ion-exchange resins, etc. Injection of bioerodible microparticulates in the vitreous for treating infections of posterior segment and the release of acceptable levels of drug up to two weeks has been demonstrated. Both corneal and non-corneal routes of drug entry in the eye from topical instillations are postulated. The in vitro and in vivo studies have shown that this dosage form holds great promise for sustained drug release in the eye. However, several formulation challenges, including production of stable suspensions, uniform dose per unit volume, efficient drug entrapment, reproducible and large scale manufacturing, uniform particle size, etc., have to be addressed. Fruitful resolution of technological challenges will result in a superior dosage form for both topical and intraocular ophthalmic application. Recent developments and future challenges of microparticulate ophthalmic drug delivery system are discussed in this review.

Pharmacological agents that modulate the wound healing process by inhibiting fibroblast proliferation may improve the success of proliferative vitreoretinopathy and glaucoma filtration surgery and may have applications in other surgical fields. It is possible that light-absorbing chemicals can be used to cause photo reactions in proliferating fibroblasts as a means of controlling this wound healing process. We present the effects of photofrin porfimer sodium (serial tenfold dilutions 1000-0.00001 micrograms/ml) on human fibroblasts from Tenon's capsule in vitro, with and without photoactivation with Argon green laser (700 mW for 1 and 5 minutes) and with bright sunlight (for 1 and 5 min). The cell density was measured on day 2 by 3H-thymidine uptake and on day 9 by means of a coulter counter, and optical density was measured in terms of the activity of the enzyme hexosaminidase. Each experiment was performed three times in quadruplicate. The counts were averaged for each drug concentration and mean cell count with a standard error as well as the 50% inhibitory doses (ID50s) were calculated. Photofrin demonstrated an inhibitory dose response curve (dark toxicity) to human fibroblasts. Concentrations greater than 100 micrograms/ml of photofrin alone completely inhibited cell growth. Concentrations less than 0.01 micrograms/ml did not have any effect on fibroblast proliferation. There was no significant log dose shift of the inhibitory effect of photofrin with the exposure to either sunlight or Argon laser. Photofrin may be used as a cytotoxic agent alone but does not appear to be activated by light to modulate subconjunctival fibroblast proliferation within the laser parameters used.