Ocular Surface Displacement with and without Contact Lenses during Non-Contact Tonometry

Purpose

To evaluate the displacement of the central ocular surface during non-contact tonometry with and without soft contact lenses and determine the factors associated with the displacement of the central ocular surface and intraocular pressure (IOP) reading changes caused by wearing soft contact lenses (CLs).

Methods

One eye each in 21 subjects was studied. The cornea was photographed using a high-speed camera at 5,000 frames/sec during non-contact tonometry without contact lenses (NCL), with -5.0 diopters (D), -0.5 D and +5.0 D CL. The displacement of the ocular surface and the factors affecting displacement at the IOP reading and maximum displacement time were investigated.

Results

The IOP readings while wearing +5 D CL were significantly higher than those obtained while wearing -5 D CL. The ocular surface displacement between +5 D CL and other groups were significantly different. A significant positive correlation was found between the ocular surface displacement of subjects at the IOP reading time and the IOP obtained with the non-contact tonometer. A significant negative correlation was found between the ocular surface curvature and the IOP obtained using the non-contact tonometer. The radius of curvature of the ocular surface affected the displacement during the IOP reading and maximum displacement time.

Conclusions

Our results indicate that soft contact lens use changes the ocular surface behavior and IOP readings during non-contact tonometry. The radius of curvature of the eye affects the ocular surface displacement and IOP readings in this situation.     

Differences between calcifuge and acidifuge plants in root exudation of low-molecular organic acids

The nature and quantity of low-molecular organic acids (LOAs) exuded by the roots of nine species of calcifuge and nine species of acidifuge wild plants from northern Europe were determined by ion chromatography. Particular attention was paid to differences between the calcifuge and the acidifuge species in the proportions of different LOAs in their root exudates. Great differences in mol% root exudation between the calcifuge and the acidifuge species were found in some acids. The calcifuge species exuded more acetic acid, the acidifuge species more oxalic acid and much more citric acid. In three calcifuge species, however, root exudation of oxalic acid was appreciable, whereas acetic acid exudation was low in these species. The phosphate- and Fe-solubilizing ability of eight LOAs in a rhizosphere limestone soil was also tested. Oxalic acid was the most efficient phosphate solubilizer and citric acid, by far, the most efficient Fe-solubilizer at the concentration (10 mM) tested. It might be hypothesized that acidifuge species use oxalate to solubilize phosphate and citrate to solubilize Fe, in limestone soil. The inability of calcifuge species to grow in limestone soil might, therefore, be due to low root exudation of these acids and, as a result, inability to solubilize phosphate and Fe in limestone soil.     

Purification and characterization of a pig intestinal alpha-limit dextrinase

Mucosa from the duodenal and jejunal regions of pig small intestine was repeatedly freeze-thaw treated to solubilize an enzyme preparation, enriched in maltase, glucoamylase and alpha-limit dextrinase activities; isomaltase and sucrase remained essentially insoluble during the treatment. Chromatographic procedures, including ion-exchange, gel filtration and hydroxylapatite chromatography of the solubilized preparation, brought to homogeneity an alpha-glucosidase active towards maltose, alpha-limit dextrins and starch in decreasing order, with only a very weak capacity to hydrolyse alpha-1,6-linkages. Michaelis constants and maximal velocities, as well as relative rates of hydrolysis of several substrates, including maltodextrins and alpha-limit dextrins, were determined and served to characterize what seems to be a rather specific alpha-1,4-glucosidase. The participation of this enzyme in the hydrolysis of alpha-limit dextrins and more generally in pathways for starch breakdown in the pig digestive tract is examined and discussed.     

Gastroretentive drug delivery system of ranitidine hydrochloride: Formulation and in vitro evaluation

The purpose of this research was to prepare a gastroretentive drug delivery system of ranitidine hydrochloride. Guar gum, xanthan gum, and hydroxypropyl methylcellulose were evaluated for gel-forming properties. Sodium bicarbonate was incorporated as a gas-generating agent. The effects of citric acid and stearic acid on drug release profile and floating properties were investigated. The addition of stearic acid reduces the drug dissolution due to its hydrophobic nature. A 3² full factorial design was applied to systemically optimize the drug release profile. The amounts of citric acid anhydrous (X₁) and stearic acid (X₂) were selected as independent variables. The times required for 50% (t₅₀) and 80% drug dissolution (t₈₀), and the similarity factor f₂ were selected as dependent variables. The results of the full factorial design indicated that a low amount of citric acid and a high amount of stearic acid favors sustained release of ranitidine hydrochloride from a gastroretentive formulation. A theoretical dissolution profile was generated using pharmacokinetic parameters of ranitidine hydrochloride. The similarity factor f₂ was applied between the factorial design batches and the theoretical dissolution profile. No significant difference was observed between the desired release profile and batches F2, F3, F6, and F9. Batch F9 showed the highest f2 (f2=75) among all the batches, and this similarity is also reflected in t₅₀ (∼214 minutes) and t₈₀ (∼537 minutes) values. These studies indicate that the proper balance between a release rate enhancer and a release rate retardant can produce a drug dissolution profile similar to a theoretical dissolution profile.     

Sustained release of an anti-glaucoma drug: demonstration of efficacy of a liposomal formulation in the rabbit eye

Topical medication remains the first line treatment of glaucoma; however, sustained ocular drug delivery via topical administration is difficult to achieve. Most drugs have poor penetration due to the multiple physiological barriers of the eye and are rapidly cleared if applied topically. Currently, daily topical administration for lowering the intra-ocular pressure (IOP), has many limitations, such as poor patient compliance and ocular allergy from repeated drug administration. Poor compliance leads to suboptimal control of IOP and disease progression with eventual blindness. The delivery of drugs in a sustained manner could provide the patient with a more attractive alternative by providing optimal therapeutic dosing, with minimal local toxicity and inconvenience. To investigate this, we incorporated latanoprost into LUVs (large unilamellar vesicles) derived from the liposome of DPPC (di-palmitoyl-phosphatidyl-choline) by the film hydration technique. Relatively high amounts of drug could be incorporated into this vesicle, and the drug resides predominantly in the bilayer. Vesicle stability monitored by size measurement and DSC (differential scanning calorimetry) analysis showed that formulations with a drug/lipid mole ratio of about 10% have good physical stability during storage and release. This formulation demonstrated sustained release of latanoprost in vitro, and then tested for efficacy in 23 rabbits. Subconjunctival injection and topical eye drop administration of the latanoprost/liposomal formulation were compared with conventional daily administration of latanoprost eye drops. The IOP lowering effect with a single subconjunctival injection was shown to be sustained for up to 50 days, and the extent of IOP lowering was comparable to daily eye drop administration. Toxicity and localized inflammation were not observed in any treatment groups. We believe that this is the first demonstration, in vivo, of sustained delivery to the anterior segment of the eye that is safe and efficacious for 50 days.     

Coaxial Electrospray of Ranibizumab-Loaded Microparticles for Sustained Release of Anti-VEGF Therapies

Age-related macular degeneration (AMD) is the leading cause of vision loss and blindness in people over age 65 in industrialized nations. Intravitreous injection of anti-VEGF (vascular endothelial growth factor) therapies, such as ranibizumab (trade name: Lucentis), provides an effective treatment option for neovascular AMD. We have developed an improved coaxial electrospray (CES) process to encapsulate ranibizumab in poly(lactic-co-glycolic) acid (PLGA) microparticles (MPs) for intravitreous injection and sustained drug release. This microencapsulation process is advantageous for maintaining the stability of the coaxial cone-jet configurations and producing drug-loaded MPs with as high as 70% encapsulation rate and minimal loss of bioactivitiy. The utility of this emerging process in intravitreous drug delivery has been demonstrated in both benchtop and in vivo experiments. The benchtop test simulates ocular drug release using PLGA MPs encapsulating a model drug. The in vivo experiment evaluates the inflammation and retinal cell death after intravitreal injection of the MPs in a chick model. The experimental results show that the drug-load MPs are able to facilitate sustained drug release for longer than one month. No significant long term microglia reaction or cell death is observed after intravitreal injection of 200 μg MPs. The present study demonstrates the technical feasibility of using the improved CES process to encapsulate water-soluble drugs at a high concentration for sustained release of anti-VEGF therapy.     

Discordant expression of the sterol pathway in lens underlies simvastatin-induced cataracts in Chbb: Thom rats

Simvastatin rapidly induced cataracts in young Chbb:Thom (CT) but not Sprague Dawley (SD) or Hilltop Wistar (HW) rats. Oral treatment for 14 but not 7 days committed CT rat lenses to cataract formation. The cholesterol to phospholipid molar ratio in lenses of treated CT rats was unchanged. Differences between strains in serum and ocular humor levels of simvastatin acid poorly correlated with susceptibility to cataracts. No significant differences were found between rat strains in the capacity of simvastatin acid to inhibit lens-basal sterol synthesis. Prolonged treatment with simvastatin comparably elevated HMG-CoA reductase protein and enzyme activity in lenses of both cataract resistant and sensitive strains. However, in contrast to SD and HW rats, where sterol synthesis was markedly increased, sterol synthesis in CT rat lenses remained at baseline. Discordant expression of sterol synthesis in CT rats may be due to inadequate upregulation of lens HMG-CoA synthase. HMG-CoA synthase protein levels, and to a much lesser extent mRNA levels, increased in lens cortex of SD but not CT rats. Because upregulation of the sterol pathway may result in increased formation of isoprene-derived anti-inflammatory substances, failure to upregulate the pathway in CT rat lenses may reflect an attenuated compensatory response to injury that resulted in cataracts.     

New poly-(3-hydroxybutyrate)-based systems for controlled release of dipyridamole and indomethacin

New poly-(3-hydroxybutyrate)-based systems for controlled release of anti-inflammatory and antithrombogenic drugs have been studied. The release occurs via two mechanisms (diffusion and degradation) operating simultaneously. Dipyridamole and indomethacin diffusion processes determine the rate of the release at the early stages of the contact of the system with the environment (the first 6-8 days). The coefficient of the release diffusion of a drug depends on its nature, the thickness of the poly-(3-hydroxybutyrate) films containing the drug, the concentrations of dipyridamole and indomethacin, and the molecular weight of the poly-(3-hydroxybutyrate). The results obtained are critical for developing systems of release of diverse drugs, thus, enabling the attainment of the requisite physiological effects on tissues and organs of humans.     

Effect of nutrient limitation on adhesion characteristics of Pseudomonas aeruginosa

Pseudomonas aeruginosa causes a variety of diseases in humans including lung and ocular infections. Infections of the cornea are usually associated with wearing contact lenses and can result in loss of vision. This study aimed to determine the effect of carbon or nitrogen limitation on the adhesion to contact lenses of a strain of Ps. aeruginosa isolated from contact lens-related corneal inflammation. Cells were grown in a continuous culture apparatus in varying levels of glucose or ammonia to effect nutrient limitation. Adhesion to contact lenses was measured as total counts and viable counts. The cell surface hydrophobicity and charge were measured using adhesion to surface-modified Sepharose. Changes in lipopolysaccharide were determined using 1D SDS-PAGE and changes in cell-surface proteins were measured using 2D gel electrophoresis. The more the cultures were nitrogen limited, the greater the increase in adhesion to unworn hydrogel contact lenses 0.3 x 10(3) - 2.2 x 10(3) cells/mm2 on Etafilon A lenses. Cells that were carbon limited showed a greater increase in adhesion to contact lenses when the lenses had been coated in artificial tears. It appeared that lipopolysaccharide may have been involved in the constitutive adhesion to unworn lenses that occurred during C-limitation, whereas changes in the outer membrane proteins contributed to the increased adhesion under nitrogen limitation, or the change in adhesion that occurred to carbon-limited cells using contact lenses coated in artificial tears. Nine cell-surface proteins appeared during nitrogen limitation with kDa/pI of 75/4.8, 4.9, 5.0; 62/5.6; 89/6.5; 38/6.4; 28/1.5; 18/6.4; 12/4.5. Any or all of these may have been involved in the increased adhesion and further experiments are underway to examine this possibility.     

Structure investigation of amphiphilic cyclopeptides in isotropic and anisotropic environments-A model study simulating peptide-membrane interactions.

It has been proposed that the membrane allows a much more efficient binding of certain small or medium-sized amphiphilic messenger molecules to their receptor, not only by accumulation of the drug, but also by induction of orientations and conformations that are much more favorable for receptor docking than structures adopted in isotropic phases. A series of eight amphiphilic cyclic peptides containing lipophilic (L-alpha-aminodecanoic acid = Ada, L-alpha-aminohexadecanoic acid = Ahd, Nhdg = N-hexadecylglycine) and hydrophilic (Lys, Asp) amino acids were synthesized and examined by means of NMR spectroscopy and molecular dynamics (MD) simulations in isotropic (CDCl3) and membrane-mimicking anisotropic (SDS/H2O) solvents to study the influence of the environment on their individual conformations. NMR data of cyclo(-Gly1-D-Asp2-Ahd3-Ahd4-Asp5-Gly6+ ++-) (C4), cyclo(-Lys1-D-Pro2-Lys3-Ada4-Pro5-Ada6-) (C5) and cyclo(-Lys1-Pro2-Lys3-Ada4-D-Pro5-Ada6-) (C6) clearly indicate that those compounds are too rigid to perform a conformational change upon transition from an isotropic to an anisotropic environment. On the other hand, the experimental data of cyclo (-Gly1-Asp2-Ahd3-Ahd4-Asp5-Gly6-) (C1), cyclo(-Asp1-Ala2-Nhdg3-Ala4-D-Asp5-) (C7), and cyclo(-D-Asp1-Ala2-Nhdg3-Ala4-Asp5-) (C8) suggest highly flexible unstructured molecules in both environments. However, for cyclo(-Asp1-Asp2-Gly3-Ahd4-Ahd5-Gly6-) (C2) we observed a structure inducing effect of a membrane-like environment. The compound populates three different conformations in SDS/H2O, whereas in CDCI3 no preferred conformation can be detected. cyclo(-D-Asp1-Asp2-Gly3-Ahd4-Ahd5-Gly6-) (C3) clearly exhibits two different conformations with a shifted beta,beta-turn motif in CDCI3 and SDS/H2O solutions. The conformational change could be reproduced in a restraint-free MD simulation using the biphasic membrane mimetic CCl4/H2O. Our results give clear evidence that membrane interactions may not only lead to structure inductions, but can also induce major conformational changes in compounds already exhibiting a defined structure in isotropic solution.     

Development and Evaluation of Sustained Release Gastroretentive Minimatrices for Effective Treatment of H. pylori Infection

In the present work, sustained release gastroretentive minimatrices of amoxicillin have been designed and optimized using central composite design. Effect of amount of xanthan gum, rate controlling polymers (HPMC K100M CR/PEO coagulant (1:1)), carbopol 974P, and gas generating couple (sodium bicarbonate/citric acid (3:1)) was studied on dependent (response) variables, i.e., buoyancy lag time, drug release at 1 h, time required for 95% drug release, swelling index, and bioadhesive strength. Minimatrices were prepared by non aqueous granulation method using solution of PVP K30 in isopropyl alcohol. All the formulations were found to contain 99.2% to 100.9% of amoxicillin per minimatrix. Optimum formulation (Formulation number AGT09) containing high level of the independent variables was having buoyancy lag time of 7 min and drug release at 1 h was 32.5%. It required 9.39 h for 95% drug release while swelling index and bioadhesive strength were 341 and 17.9 dyn/cm², respectively. This formulation was said to be optimum because it has minimum buoyancy lag time, requires maximum time for 95% drug release, and has higher bioadhesive capabilities. In vitro results of an optimized formulation indicate its sustained drug release and gastric retention capability, which may be very useful for effective treatment of H. pylori infection.     

Optimization of citric acid production from Candida lipolytica Y-1095 using n-paraffin

Currently, the majority of worldwide microbial production of citric acid utilizes Aspergillus niger in a carbohydrate based submerged fermentation. Due to their high carbon content, hydrocarbons also have the potential of producing high concentrations of citric acid. Initial lab experiments conducted using 1875 ml batch fermentations with n-paraffin found that Candida lipolytica NRRL-Y-1095 assimilated the feedstock and had a citric acid productivity of 47 mg l(-1) h(-1). To determine the optimum level of initial biomass concentration, n-paraffin concentration, iron concentration and temperature for the production of citric acid, a central composite design was developed using 200 ml batch fermentations. The design involved conducting 31 batch fermentations under various combinations of high and low values of these four parameters. From this investigation empirical models were developed describing the interactions between the experimental parameters and citric acid production. It was found that the maximum concentration of citric acid produced was 9.8 g l(-1) and the optimum levels of each parameter for citric acid production were, 10--12% volume for initial biomass concentration, 10--15% volume for n-paraffin concentration, 10 mg l(-1) for ferric nitrate concentration, and 26--30 degrees C for temperature.     

Ultrasonic model and system for measurement of corneal biomechanical properties and validation on phantoms

Non-invasive measurement of biomechanical properties of corneas may provide important information for ocular disease management and therapeutic procedures. An ultrasonic non-destructive evaluation method with a wave propagation model was developed to determine corneal biomechanical properties in vivo. In this study, we tested the feasibility of the approach in differentiating the mechanical properties of soft contact lenses as corneal phantoms. Three material types of soft contact lenses (six samples in each group) were measured using a broadband ultrasound transducer. The ultrasonic reflections from the contact lenses were recorded by a 500MHz/8-bit digitizer, and displayed and processed by a PC. A reference signal was recorded to compute the normalized power spectra using Fast Fourier Transformation. An inverse algorithm based on least-squares minimization was used to reconstruct three parameters of the contact lenses: density, thickness, and elastic constants lambda+2micro. The thickness of each sample was verified using an electronic thickness gauge, and the averaged density for each type of lenses was verified using Archimedes' principle and manufacturer's report. Our results demonstrated that the ultrasonic system was able to differentiate the elastic properties of the three types of the soft contact lenses with statistical significance (P-value<0.001). The reconstructed thicknesses and densities agreed well with the independent measurements. Our studies on corneal phantoms indicated that the ultrasonic system was sensitive and accurate in measuring the material properties of cornea-like structures. It is important to optimize the system for in vivo measurements.     

The role of bacterial biofilms in ocular infections

There is increasing evidence that bacterial biofilms play a role in a variety of ocular infections. Bacterial growth is characterized as a biofilm when bacteria attach to a surface and/or to each other. This is distinguished from a planktonic or free-living mode of bacterial growth where these interactions are not present. Biofilm formation is a genetically controlled process in the life cycle of bacteria resulting in numerous changes in the cellular physiology of the organism, often including increased antibiotic resistance compared to growth under planktonic conditions. The presence of bacterial biofilms has been demonstrated on many medical devices including intravenous catheters, as well as materials relevant to the eye such as contact lenses, scleral buckles, suture material, and intraocular lenses. Many ocular infections often occur when such prosthetic devices come in contact with or are implanted in the eye. For instance, 56% of corneal ulcers in the United States are associated with contact lens wear. Bacterial biofilms may participate in ocular infections by allowing bacteria to persist on abiotic surfaces that come in contact with, or are implanted in the eye, and by direct biofilm formation on the biotic surfaces of the eye. An understanding of the role of bacterial biofilm formation in ocular infections may aid in the development of future antimicrobial strategies in ophthalmology. We review the current literature and concepts relating to biofilm formation and infections of the eye.     

碱胁迫下耐碱植物星星草体内柠檬酸特异积累现象

对碱胁迫(0-175 mmol/L Na2CO3)下星星草(Puccinellia tenuiflora (Griseb.) Scribn.et Merr.)体内柠檬酸的积累规律及其相关胁变指标进行分析测定.实验结果证明:积累柠檬酸是星星草对碱胁迫特有的生理反应.盐胁迫(0-400 mmol/L NaCl)下,柠檬酸含量反而稍有下降.柠檬酸积累量随碱胁迫强度增大而增大,低胁迫强度时积累量上升缓慢,当胁迫强度大于100 mmol/L Na2CO3时,积累量明显上升.柠檬酸积累与胁迫时间之间呈直角曲线关系,一定胁迫强度下胁迫4 h后即可测出柠檬酸含量明显上升,约48 h后渐趋最大值.碱胁迫144 h后星星草各部位中柠檬酸含量从高到低的顺序依次是老叶、成熟叶、老叶鞘、幼叶鞘、幼茎、老茎和幼叶.成熟叶中柠檬酸随碱胁迫强度增大而逐渐上升,老叶和叶鞘中的柠檬酸在碱胁迫强度大于125 mmol/L后急剧上升,茎中柠檬酸含量无明显增高,幼叶中柠檬酸含量基本不变.实验证明,碱胁迫下积累的主要是柠檬酸,其他有机酸无明显变化.     

Simultaneous Removal of Lindane,Lead and Cadmium from Soils by Rhamnolipids Combined with Citric Acid

This study investigated the performance of rhamnolipids-citric acid mixed agents in simultaneous desorption of lindane and heavy metals from soils. The capacity of the mixed agents to solubilize lindane, lead and cadmium in aqueous solution was also explored. The results showed that the presence of citric acid greatly enhanced the solubilization of lindane and cadmium by rhamnolipids. A combined effect of the mixed agents on lindane and heavy metals removal from soils was observed. The maximum desorption ratios for lindane, cadmium and lead were 85.4%, 76.4% and 28.1%, respectively, for the mixed agents containing 1% rhamnolipidsand 0.1 mol/L citric acid. The results also suggest that the removal efficiencies of lead and cadmium were strongly related to their speciations in soils, and metals in the exchangeable and carbonate forms were easier to be removed. Our study suggests that the combining use of rhamnolipids and citric acid is a promising alternative to simultaneously remove organochlorine pesticides and heavy metals from soils.     

Production of citric acid from starch-hydrolysate by Aspergillus niger

The present investigation explored the possible use of a rarely used agro-industrial by-product, maize starch-hydrolysate, for economic production of citric acid. To achieve this, seventeen strains of Aspergillus niger were screened for their capacity to produce citric acid using starch-hydrolysate as a substrate. The most efficient strain, ITCC-605 was selected for further improvement in citric acid content by mutation. Mutants developed by treatment with EMS and UV, singly and in combination, produced citric acid in the range of 0.51-64.7 g kg(-1) of glucose consumed. The mutant UE-1 produced the maximum citric acid which was about 130 times more than that produced by the parent strain, ITCC-605. For further increase in citric acid production from this substrate, the cultural conditions were optimized: concentration of starch-hydrolysate, 15% (glucose equivalent); ammonium nitrate, 0.25%; KH2PO4, 0.15%; nicotinic acid, 0.0001% and initial pH of 2.0. Under these conditions, the mutant strain UE-1 yielded 490 g citric acid kg(-1) of glucose consumed in 8 days of incubation at 30 degrees C. The productivity of 341 mgl(-1)h(-1) corresponded to 49% substrate conversion to citric acid.     

Oxygen requirements for growth and citric acid production of Yarrowia lipolytica

During continuous cultivation of Yarrowia lipolytica N 1, oxygen requirements for growth and citric acid synthesis were found to depend on the iron concentration in the medium. A coupled effect of oxygen and iron concentrations on the functioning of the mitochondrial electron transport chain in Y. lipolytica N 1 was established. Based on the results obtained in continuous culture, conditions for citric acid production in a batch culture of Y. lipolytica N 1 were proposed. At relatively low pO(2) value and a high iron concentration, citric acid accumulation was as high as 120 g l(-1); the specific rate of citric acid synthesis reached 120 mg citric acid (g cells h)(-1). The mass yield coefficient was 0.87 and the energy yield coefficient was 0.31.     

An adaptable HPLC method for the analysis of frequently used antibiotics in ocular samples

Four different antibiotics, delivered individually to rabbit eyes via hydrophilic intraocular lenses soaked in the drug solution prior to implantation, were measured in aqueous and vitreous humor samples from the eyes. To meet this analytical need, we developed a sensitive, high performance liquid chromatographic (HPLC) method for measuring the concentrations of moxifloxacin, gatifloxacin, linezolid, and cefuroxime in the ocular tissue. Separations were carried out on a LichroSpher RP-18 column, maintained at room temperature. The fluoroquinolones were eluted with a mobile phase consisting of 20% acetonitrile, in 0.1% trifluoroacetic acid (pH 3.0) with 30 mM tetrabutylammonium chloride. Linezolid and cefuroxime were eluted with 25% acetonitrile in 25 mM Na acetate buffer, pH 5.0. All elutions were isocratic. With ultraviolet detection, the lower limit of quantitation (LLOQ) for these compounds approached 1 ng (on-column injection). By using fluorescence detection, the LLOQ for the fluoroquinolones improved to 200 pg. The overall accuracy of the method was ≥90%. With minor modifications, the method was optimized for each of the agents, and the resulting analytical sensitivity made the method suitable for clinical investigations of the ocular penetration of these drugs.