Surface chemistry studies present criteria for preclinical in vitro molecular scale characterization of the interactions between eyedrop compounds and TF constituents.

The surface chemistry approach used in this study provided molecular-scale insights into the detrimental effect of BAC on TF, which well explain the TF instability and corneal epithelial barrier dysfunction after exposure to BAC in the in vivo human eye.

a b s t r a c tThe surface interactions of Meibomian gland secretion (MGS) with polar lipid (PL), Egg Sphingomyelin (SM) or Dipalmitoylphosphatidylcholine (DPPC), are studied in mixed pseudo-binary films formed at the air/water interface of Langmuir surface balance. The behavior of the mixed films during slow quasi-equilibrium compression and during fast dynamic compression-decompression is registered by measurements of surface pressure and surface potential, and by monitoring film morphology with Brewster Angle Microscopy (BAM). Quasi-equilibrium compression isotherms are used to calculate the excess Gibbs and Helmholtz energy of mixing between MGS and PLs and thus to evaluate the interactions between the lipid compounds at the interface. The effects of PLs on the mixed film's elastic moduli of area compressibility, morphology and capability to attain high surface pressures are also examined.PLs interact with MGS with different strength and in different manner: MGS-SM interaction is weak and might lead to interfacial disaggregation of the thick meibium domains when SM is in excess, while MGS-DPPC interaction is strong and results in the formation of thick lipid aggregates. Both PLs increase the mixed films reciprocal compressibility and capability to achieve higher surface pressures. The results demonstrate that in vitro studies of the surface interactions between MGS and PLs might be beneficial in the selection of PLs for artificial tear formulations and for examination on molecular scale of the possible role of PLs at the ocular surface.

Hyaluronic acid (HA) is a non-surface active water soluble anionic polyelectrolyte found in sub-nanomolar levels in human tears and implemented in substitutes of human tears' aqueous layer. In the current work we studied the interactions of high molecular weight (M w 1 Â 10 6 Da) HA with films of ocular surface lipids and investigated the potential of HA to modify the interactions of the lipid films with the low M w cationic surfactant dodecyldimethylbenzylammonium chloride (C12-BAC) known for its adverse effects on tear film compounds. The interactions of HA and/or C12-BAC with meibomian and corneal lipid films were examined using a Langmuir surface balance. The film morphology was monitored by Brewster Angle Microscopy. The HA/C12-BAC interactions at the air/water interface and in the solution bulk were also examined. HA interacted with meibomian lipids and enhanced the structure and the rheological properties of the meibum films. HA bound C12-BAC in bulky polymer/surfactant complexes and at $0.1% HA neutralized the capability of C12-BAC to penetrate the lipid layers and to disrupt their integrity and viscoelasticity. The results were correlated with the capability of HA to maintain the viability of C12-BAC treated corneal cells. Our study suggests a possible novel implementation of high M w anionic polyelectrolytes like HA: the polymers can be instilled on the ocular surface together with cationic surfactant containing drugs, and increase the biocompatibility of the ophthalmic formulations.A molecular scale mechanism is proposed for the interactions of HA with tear lipids and cationic surfactants.

A new strain Renibacterium salmoninarum 27BN was isolated for its capacity to utilize nhexadecane as sole substrate. Growth on n-hexadecane was accompanied with the production of glycolipid surface active substances detected by surface pressure lowering and emulsifying activity. Glycolipid detection by thin layer chromatography and infrared spectra analyses showed for the first time that Renibacterium salmoninarum 27BN secretes the two rhamnolipids RLL and RRLL typical for Pseudomonas aeruginosa. Growth of Renibacterium salmoninarum 27BN on n-hexadecane depended on the bioavailability of the substrate and the secreted rhamnolipids appeared to be efficient in increasing hexadecane availability for the cells.

The concentration of phospholipids in the AF is obviously a critical parameter as to the formation of stable BFF. The fact that from a certain phospholipid concentration upward the possibility for BFF formation correlates 100% with fetal lung maturity (clinical result in Table I) suggests the idea that the Newton black film is suitable for use as a model in investigations on the alveolar surface and the alveolar stability.The correlation between the test and the clinical results for the 182 samples reported in this paper is based on only one (3.4-fold) statistically obtained and tentatively chosen dilution of the AF samples. In a separate paper we will report the reliability of the method in predicting the clinical result at a wide range of dilutions of the AF samples (from 2-to 8-fold) and the correlation between the cutoff dilutions and the gestational age. Our preliminary results imply that a dilution other than (but near to) 3.4 may be expected which will "recognize" mature and immature samples in a better way and will, therefore, improve the reliability of the method.The advantages of the method presented here are as follows: high reliability of the prediction for both the mature and the immature samples; rapidity of determination (the test result is obtained within 30 min); ease of determination (only a reflected light microscope is necessary); simplicity of determination (the test result is straightforward and no special qualification of the clinician is necessary); use of available reagents (NaCl and ethanol); use of small volumes of AF (0.5 mL is quite enough to obtain the test result); availability and low cost of the test.By now the BFF method has been introduced in the largest hospital in Sofia (The Research Institute of Obstetrics and Gynecology at the Medical Academy-Sofia) and in some other larger hospitals in Bulgaria where it shows good results. It can be easily applied in small hospitals, as well.In perspective the method can be developed to indicate not only the maturity or the immaturity of the fetal lung but also to evaluate the "degree" of maturity or immaturity. The value of the maximal dilution at which single AF samples are still able to give BFF could possibly be used as a criterion. Another appropriate dilution could be found to predict fetal lung maturity in cases of pathological pregnancies (diabetes, RH isoimmunization, etc.). Sample contamination by blood and meconium might influence the test results too. Investigations aiming to elucidate these points are in progress.

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