Journal of ocular pharmacology最新文献

Muscarinic agonist-induced contraction of the ciliary muscle is generally believed to increase aqueous outflow facility and effect accommodation. We used cultured human ciliary muscle cells as a model to study the muscarinic receptor subtype(s) involved in the contractile response of the muscle. Thus, a single cell contraction assay for these muscle cells was developed. And since agonist-induced contraction of smooth muscles is expected to involve the activation of phospholipase C (PLC), we also monitored the PLC activity in these cells. Carbachol caused contraction of the muscle cells in a dose-dependent and time-dependent manner with an estimated EC50 of 1-3 microM. The contractile effect of 100 microM carbachol was antagonized by pretreatment of atropine (1 microM) and 4DAMP (10 nM, antagonist selective for the M1 and M3 receptors) but not by pirenzepine (10 microM, antagonist selective for the M1 receptor), suggesting the involvement of the M3 but not the M1 muscarinic receptor. M3 receptor is also essential for the carbachol-induced PLC activation in the ciliary muscle cells, as indicated by the activity profiles of receptor subtype selective antagonists. For example, the stimulative effect of carbachol (EC50 = 20 microM) was antagonized by pirenzepine (pKi = 6.8), HHSiD (pKi = 7.6), 4DAMP (pKi = 9.5) and methoctramine (pKi < 6). Thus, these results indicate that an M3-like receptor subtype is essential in mediating the muscarinic agonists-induced functional changes, such as PLC activation or muscle contraction, in the ciliary muscle.

PGE2 binding sites or receptors of porcine ciliary nonpigmented epithelial (NPE) and pigmented epithelial (PE) membranes were solubilized with detergents (CHAPS and Triton X100). From the Scatchard plots of PGE2 binding to CHAPS-solubilized proteins, the Kd and Bmax values were calculated to be 35 nM and 470 fmol/mg protein for NPE protein and 65 nM and 430 fmol/mg protein for PE protein, respectively. On the basis of the Kd and Bmax values, the solubilized receptor proteins correspond to PGE2 binding sites of the membranes which have previously been shown to be coupled to adenylate cyclase inhibition. For both NPE and PE proteins, the order of binding potency was PGE2 > PGF2 alpha > PGD2. By gel filtration chromatography of NPE and PE proteins, the molecular mass of the major PGE2 binding peak was estimated to be about 150 KDa when solubilized in CHAPS and 46 KDa for Triton X100 extracts. The Bmax values of membrane-associated binding proteins were increased by GTP, indicating a close association of the PGE2 binding sites with a GTP-binding protein. However, GTP did not affect the Bmax values of detergent-solubilized receptor proteins.

Azithromycin was orally administered to Dutch-belted rabbits following extracapsular lens extraction in one eye. At various times the animals were sacrificed, and serum and ocular tissues were obtained for drug level determination by HPLC-EC. Following a single dose, peak levels of drug in ocular tissues were measured within 8 hours (cornea > 0.5 micrograms/g [15mg/kg]; > 1.5 micrograms/g [3Omg/kg]). Highest levels were obtained in iris and ciliary body ( > 15 micrograms). Measurable tissue levels persisted for at least 120 hours. Trough levels increased proportionately during drug multiple dose administration. Five days following five daily 15mg/kg doses, corneal levels exceeded 0.5 micrograms/g, and iris and ciliary levels were higher than 15 micrograms/g. Aqueous humor and serum levels were equivalent. Vitreous humor levels, though higher than aqueous humor, were consistently < 1 microgram/ml. Extracapsular cataract extraction did not significantly affect drug uptake.

Intravitreal daunomycin (D) effectively suppresses cellular proliferation in experimental proliferative vitreoretinopathy (PVR) but has a narrow therapeutic safety range. Studies were undertaken to reduce toxicity of D by preparing a slow-release implant using polysulfone capillary fiber (PCF). Fabrication of the implant involved loading PCF with 1% D in tristearin (w/w), an excipient with diffusion-retardant properties. Two dose levels of the PCF-D device (15 micrograms and 30 micrograms/device) were prepared and sterilized prior to use. To examine the kinetics and efficacy of the device, rabbits were randomized and eyes were implanted as follows: 1) control group (PCF vehicle); 2) PCF-D (15 micrograms/device); 3) PCF-D (30 micrograms/device). Immediately after implantation, all eyes received an intravitreal injection of 2.5 x 10(5) retinal pigmented epithelial (RPE) cells. Thereafter, tractional retinal detachments (TRD) were graded by ophthalmoscopic examination. Also, fluorophotometry scanning from the retina to the anterior chamber was performed to determine the intraocular bioavailability of D. Results showed a therapeutically sustained level of D up to 21 days after device implantation. Midvitreous concentration of D was greater in group 3 than group 2 at all time points examined, indicating a dose-proportional increase in D release. Results of the PVR study showed that by 7 days after treatment, all eyes implanted with the PCF vehicle developed stage 2 TRD or greater; only 1 eye in each of groups 2 and 3 developed stage 2. By 2 weeks, most eyes in groups 2 and 3 remained in stages 1 and 2 with only 2 eyes progressing to stages 3 and 4 TRD. By 5 weeks, all eyes in group 1 showed stages 4 and 5 TRD, while most eyes in groups 2 and 3 remained in stages 1 and 2. The device with 30 micrograms D was more effective in preventing TRD. In conclusion, these data indicate that PCF can reduce the toxicity of D and may be a useful implant for treatment of PVR.

In order to characterize the inflammatory response to corneal infection by Pseudomonas aeruginosa, ocular cytokine and arachidonic acid metabolite levels were determined in the C57BL/6J strain of mice. The effects of topical anti-inflammatory drugs on the ability of the mice to clear viable P. aeruginosa from the eyes during the 12 day infection period was also examined. Ocular IL-1 alpha, IL-6, and TNF-alpha were detected over an 11 day time period. Little or no bacteria, as determined by quantitative plate counts, was detected after this time period. The kinetics of the cytokine production varied from one another, with an immediate release of peak levels of IL-1 alpha within 24 hours after infection which did not begin to approach baseline until 9 to 11 days after infection. Five to ten-fold lower concentrations of IL-6 and TNF-alpha were detected. IL-6 levels were induced at 24 hours after infection but there was essentially no distinct peak time-point. Peak levels of TNF-alpha were detected at 6 days post-infection. The kinetics of arachidonic acid metabolite release from infected eyes were also examined. Peak levels of PGE2 and TxB2 were observed at 6 days post-infection whereas peak LTB4 levels were determined at 3 days post-infection. Topical treatment of infected eyes with the two anti-inflammatory drugs, prednisolone or quercetin, resulted in higher ocular bacterial levels throughout the infection.

In order to reduce the intraocular pressure antiglaucoma drugs must penetrate into the inner eye. Ocular bioavailability is determined by the ability of drug to penetrate through the cornea and conjunctiva/sclera, and on the other hand, by its elimination from the conjunctival sac. Major part of this elimination is by systemic drug absorption via conjunctiva. Typically conjunctival systemic absorption of drugs is an order of magnitude greater than their ocular absorption. In addition substantial systemic absorption of ophthalmic drugs takes place via nasal mucosa. Systemic absorption of antiglaucoma drugs like beta blocking agents may cause systemic side-effects. The risk of systemic side-effects might be decreased by increasing the ocular/systemic ratio of drug absorption. Several approaches can be used to improve ocular/systemic drug absorption ratio. Firstly, corneal drug permeability is improved. This can be done using different formulations or prodrug derivatives. Secondly, systemic absorption can be decreased e.g. with kinetic drug interactions or drug formulations. Thirdly, the rate of drug delivery can be changed thereby affecting especially the peak concentrations of drug in systemic circulation. Different methods for improvement of ocular delivery relative to the systemic absorption of antiglaucoma drugs are summarized and the impact of systemic pharmacokinetics on the viability of each approach is discussed.

Poor bioavailability of ophthalmic solutions caused by dilution and drainage from the eye can be overcome by using in situ-forming ophthalmic drug delivery systems prepared from polymers that exhibit reversible phase transitions. Joshi et al. (1), have demonstrated that aqueous compositions that reversibly gel in response to simultaneous variations in at least two physical parameters, such as temperature, pH, and ionic strength, can be formed by appropriate combinations of macromolecular polymers which exhibit reversible gelation properties. In the present study, the rheological characterization of such a system, prepared by a combination of Carbopol (C) and methyl cellulose (MC), was carried out at two different pH (4.0 and 7.4) and temperatures (25 and 37 degrees C) by rotational cone and plate viscometry. The shear stress (tau) vs. shear rate (D) flow curves of the aqueous polymer solutions indicated a pseudoplastic behavior, with a yield point. An increase in pH from 4.0 to 7.4, or temperature from 25 to 37 degrees C, resulted in an increase in viscosity (eta), tau, and yield point, the magnitude of changes being highest when both the parameters were altered simultaneously. An increase in concentration of either C or MC, or an increase in MC molecular weight results in an increase in eta, tau, and yield point. Among the compositions studied, a solution containing 1.5% MC 0.3% C was found to have low eta, and formed a strong gel under simulated physiological conditions. Such a system can be formulated as drug containing liquid suitable for administration by instillation into the eye, which upon exposure to physiological conditions will shift to the gel (semi-solid) phase, thus increasing the precorneal residence time of the delivery system and enhancing ocular bioavailability.

Iontophoresis has been utilized in the field of ophthalmology for many years. Present application of this technique has diminished considerably and few clinicians are currently familiar with its use. This review aims to educate the reader regarding the essential features of this procedure and to discuss the past and future role of iontophoresis in ocular drug delivery.

For patients with conditions requiring chronic rather than acute therapy, the advantages of collagen shields in providing high and sustained levels of drugs and/or lubricants to the cornea are outweighed by the difficulty of insertion of the shield and the problem of blurred vision. We have developed a delivery system in which collagen pieces suspended in a viscous vehicle can be instilled into the lower forniceal space, thereby simplifying application and reducing blurring of vision. The collagen pieces (Collasomes) can be formulated with various constituents such as antibiotics or cyclosporine, or with chemical alterations such as the inclusion of a lipid (Lacrisomes) for the treatment of dry eyes. In the normal eyes of volunteers, Collasomes hydrated in a solution of sodium fluorescein and suspended in a methylcellulose vehicle as a model for delivery of water-soluble drugs produced fluorescein concentrations 17 to 42 times higher in the cornea and 6 to 8 times higher in the aqueous humor, compared with fluorescein-containing vehicle alone. In a preliminary controlled study, 76% of patients with moderately severe keratoconjunctivitis sicca (KCS) preferred Lacrisomes to the vehicle control because of a more soothing effect and longer duration of comfort. All preparations were well tolerated by all study subjects. Current studies involve improving drug delivery by chemically modifying the collagen molecule to slow diffusion of the drug from the Collasome matrix, as well as varying the amount of cetyl alcohol and combining it with modified collagen in Lacrisomes to maximize comfort in patients with dry eyes.

Pharmacological studies on pirenzepine (PZ), 4-diphenylacetoxy-N-methyl-piperidine (4-DAMP) and AFDX-116 antagonism of carbachol (CCh)-induced contraction, inositol trisphosphate (IP3) production and cAMP formation revealed the involvement of M3 receptors in these responses. The PA2 values for PZ and 4-DAMP antagonism to CCh-induced contraction were 7.1 and 9.0, respectively, and AFDX-116 had no effect on these responses. Further, 4-DAMP was a much more potent inhibitor than PZ of CCh-stimulation of IP3 production and cAMP formation. Both L-type calcium channel blockers, which inhibit Ca2+ influx, and BAPTA, an intracellular calcium chelator, inhibited these biochemical and pharmacological responses due to CCh. It is concluded that both intracellular and extracellular Ca2+ mobilization are involved in muscarinic stimulation of cAMP production, and that M3 receptors are coupled to the activation of both phospholipase C and adenylate cyclase in this tissue. The data presented here are consistent with previous work that stimulation of muscarinic receptors in dog iris sphincter with CCh (> 5 microM) increases intracellular cAMP levels.