Interaction between rose bengal and different protein components

Photo-induced protein oxidation: mechanisms, consequences and medical applications

Irradiation from the sun has played a crucial role in the origin and evolution of life on the earth. Due to the presence of ozone in the stratosphere most of the hazardous irradiation is absorbed, nonetheless UVB, UVA, and visible light reach the earth’s surface. The high abundance of proteins in most living organisms, and the presence of chromophores in the side chains of certain amino acids, explain why these macromolecules are principal targets when biological systems are illuminated. Light absorption triggers the formation of excited species that can initiate photo-modification of proteins. The major pathways involve modifications derived from direct irradiation and photo-sensitized reactions. In this review we explored the basic concepts behind these photochemical pathways, with special emphasis on the photosensitized mechanisms (type 1 and type 2) leading to protein oxidation, and how this affects protein structure and functions. Finally, a description of the photochemical reactions involved in some human diseases, and medical applications of protein oxidation are presented.

Binding of rose bengal to lysozyme modulates photooxidation and cross-linking reactions involving tyrosine and tryptophan

This work examined the hypothesis that interactions of Rose Bengal (RB^2-) with lysozyme (Lyso) might mediate type 1 photoreactions resulting in protein cross-linking even under conditions favoring ¹O₂ formation. UV-visible spectrophotometry, isothermal titration calorimetry (ITC), and docking analysis were employed to characterize RB^2--Lyso interactions, while oxidation of Lyso was studied by SDS-PAGE gels, extent of amino acid consumption, and liquid chromatography (LC) with mass detection (employing tryptic peptides digested in H₂¹⁸O and H₂O). Docking studies showed five interaction sites including the active site. Hydrophobic interactions induced a red shift of the visible spectrum of RB^2- giving a K_d of 4.8 μM, while data from ITC studies, yielded a K_d of 0.68 μM as an average of the interactions with stoichiometry of 3.3 RB^2- per Lyso. LC analysis showed a high consumption of readily-oxidized amino acids (His, Trp, Met and Tyr) located at different and diverse locations within the protein. This appears to reflect extensive damage on the protein probably mediated by a type 2 (¹O₂) mechanism. In contrast, docking and mass spectrometry analysis provided evidence for the generation of specific intra- (Tyr23-Tyr20) and inter-molecular (Tyr23-Trp62) Lyso cross-links, and Lyso dimer formation via radical-radical, type 1 mechanisms.

Dye-Free Porcine Model of Experimental Branch Retinal Vein Occlusion: A Suitable Approach for Retinal Proteomics

Branch retinal vein occlusion induces complex biological processes in the retina that are generated by a multitude of interacting proteins. These proteins and their posttranslational modifications can effectively be studied using modern proteomic techniques. However, no method for studying large-scale protein changes following branch retinal vein occlusion has been available until now. Obtainment of retinal tissue exposed to branch retinal vein occlusion is only available through experimental animal models. Traditional models of experimental branch retinal vein occlusion require the use of Rose Bengal dye combined with argon laser photocoagulation. The use of Rose Bengal dye is problematic in proteomic studies as the dye can induce multiple protein modifications when irradiated. This paper presents a novel technique for proteomic analysis of porcine retinal tissue with branch retinal vein occlusion combining a dye-free experimental model with label-free liquid chromatography mass spectrometry based proteomics.

Optimization of silk films as substrate for functional corneal epithelium growth

The corneal epithelium is the first cellular barrier to protect the cornea. Thus, functional tissue engineering of the corneal epithelium is a strategy for clinical transplantation. In this study, the optimization of silk films (SFs) as substrates for functional human corneal epithelium growth was investigated with primary human corneal epithelial cells on SFs, poly-D-lysine (PDL) coated SFs, arginine-glycine-aspartic acid (RGD) modified SFs and PDL blended SFs. PDL coated SFs significantly promoted cell adhesion at early phases in comparison to the other study groups, while PDL blended SF significantly promoted cell migration in a "wound healing" model. All film modifications promoted cell proliferation and viability, and a multi-layered epithelium was achieved in 4 weeks of culture. The epithelia formed were tightly apposed and maintained an intact barrier function against rose bengal dye penetration. The results suggested that a differentiated human corneal epithelium can be established with primary corneal epithelial cells on SFs in vitro, by optimizing SF composition with PDL.

Topical delivery and photodynamic evaluation of a multivesicular liposomal Rose Bengal

We investigated the pharmaceutical and physicochemical properties of different multivesicular liposome (MVL) formulations for the delivery of Rose Bengal (RB) into skin layers for topical photodynamic therapy. The drug content, uniformity, spreadability and release kinetics of the optimum hydrogel formulation were studied. Skin penetration of the prepared gels was studied in albino mice using fluorescence microscopy and the photodynamic properties were evaluated. The loading efficiency of MVL ranged from 56% to 79%. In vitro RB release from MVL followed Higuchi's diffusion mechanism and the amount of RB released after 2 h from the optimum MVL (comprising D,L-dipalmitoylphosphatidyl choline, cholesterol and tripalmitin at a molar ratio of 1:0.7:0.1, respectively) was 2.5-fold higher than from the other MVL formulations. The type and concentration of phospholipids did not significantly (p > 0.05) affect vesicle size but significantly (p < 0.05) increased the encapsulation capacity and thermal properties. RB in hydrogel was spreadable and uniformly distributed. Fluorescence microscopy 30 min after topical application to the skin of mice showed that RB loaded into MVL was significantly (p < 0.05) more distributed into the dermal layers than free RB which accumulated in the epidermis. This finding was confirmed by the presence of superficial necrotic cells in histological sections of skin treated with free RB and the presence of RB in the deep dermal layers of sections of skin treated with the MVL-RB formulation and irradiated for 10 min with light of wavelength 550 nm from a light emitting diode at 80 mW. MVL hydrogel is a promising topical delivery system which allows successful delivery of RB into skin layers for different photodynamic therapies in dermatology.

Still confused about rose bengal?

We have surveyed the ophthalmic literature of the last five years in an attempt to evaluate the use and usefulness of Rose Bengal staining as an aid to differential diagnosis in dry eyes. Included both as a criterion and as an adjunct measure of disease progression, Rose Bengal scores of patients with different dry eye conditions overlap, sometimes to a considerable extent. A mechanistic link between staining with this dye and disease etiology is unlikely; however, Rose Bengal could be a surrogate marker of changes in ocular surface physiology. The question whether the extent and pattern of staining with Rose Bengal provide the clinician with information not available from other tests, and in particular from fluorescein staining of the ocular surface, has to be answered positively, though the nature of this information is not clearly understood. A more widespread recognition that Rose Bengal is not a vital dye is necessary in order not to bias the interpretation of experimental results.

Release of membrane-associated mucins from ocular surface epithelia

PURPOSE

Three membrane-associated mucins (MAMs)--MUC1, MUC4, and MUC16--are expressed at the ocular surface epithelium. Soluble forms of MAMs are detected in human tears, but the mechanisms of their release from the apical cells are unknown. The purpose of this study was to identify physiologic agents that induce ocular surface MAM release.

METHODS

An immortalized human corneal-limbal epithelial cell line (HCLE) expressing the same MAMs as native tissue was used. An antibody specific to the MUC16 cytoplasmic tail was developed to confirm that only the extracellular domain is released into the tear fluid or culture media. Effects of agents that have been shown to be present in tears or are implicated in the release or shedding of MAMs in other epithelia (neutrophil elastase, tumor necrosis factor [TNF]), TNF-alpha-converting enzyme, and matrix metalloproteinase-7 and -9) were assessed on HCLE cells. HCLE cell surface proteins were biotinylated to measure the efficiency of induced MAM release and surface restoration. Effects of induced release on surface barrier function were measured by rose bengal dye penetrance.

RESULTS

MUC16 in tears and in HCLE-conditioned medium lacked the cytoplasmic tail. TNF induced the release of MUC1, MUC4, and MUC16 from the HCLE surface. Matrix metalloproteinase-7 and neutrophil elastase induced the release of MUC16 but not of MUC1 or MUC4. Neutrophil elastase removed 68% of MUC16, 78% of which was restored to the HCLE cell surface 24 hours after release. Neutrophil elastase-treated HCLE cells showed significantly reduced rose bengal dye exclusion.

CONCLUSIONS

Results suggest that the extracellular domains of MUC1, MUC4, and MUC16 can be released from the ocular surface by agents in tears. Neutrophil elastase and TNF, present in higher amounts in the tears of patients with dry eye, may cause MAM release, allowing rose bengal staining.

Mucin characteristics of human corneal-limbal epithelial cells that exclude the rose bengal anionic dye

PURPOSE

Rose bengal is an organic anionic dye used to assess damage of the ocular surface epithelium in ocular surface disease. It has been proposed that mucins have a protective role, preventing rose bengal staining of normal ocular surface epithelial cells. The current study was undertaken to evaluate rose bengal staining in a human corneal-limbal epithelial (HCLE) cell line known to produce and glycosylate membrane-associated mucins.

METHODS

HCLE cells were grown to confluence in serum-free medium and switched to DMEM/F12 with 10% serum to promote differentiation. Immunolocalization of the membrane-associated mucins MUC1 and MUC16 and the T-antigen carbohydrate epitope was performed with the monoclonal antibodies HMFG-2 and OC125 and jacalin lectin, respectively. To assess dye uptake, cultures were incubated for 5 minutes with 0.1% rose bengal and photographed. To determine whether exclusion of negatively charged rose bengal requires a negative charge at the cell surface, cells were incubated with fluoresceinated cationized ferritin. The effect of hyperosmotic stress on rose bengal staining in vitro was evaluated by increasing the ion concentration (Ca+2 and Mg+2) in the rose bengal uptake assay.

RESULTS

The cytoplasm and nucleus of confluent HCLE cells cultured in media without serum, lacking the expression of MUC16 but not MUC1, as well as human corneal fibroblasts, which do not express mucins, stained with rose bengal. Culture of HCLE cells in medium containing serum resulted in the formation of islands of stratified cells that excluded rose bengal. Apical cells of the stratified islands produced MUC16 and the T-antigen carbohydrate epitope on their apical surfaces. Colocalization experiments demonstrated that fluoresceinated cationized ferritin did not bind to these stratified cells, indicating that rose bengal is excluded from cells that lack negative charges. Increasing the amounts of divalent cations in the media reduced the cellular area protected against rose bengal uptake.

CONCLUSIONS

These results indicate that stratification and differentiation of corneal epithelial cells, as measured by the capacity to produce the membrane-associated mucin MUC16 and the mucin-associated T-antigen carbohydrate on their apical surfaces provide protection against rose bengal penetrance in vitro and suggest a role for membrane-associated mucins and their oligosaccharides in the protection of ocular surface epithelia.

Tear lipocalin: evidence for a scavenging function to remove lipids from the human corneal surface

PURPOSE

Lipid contamination of the cornea may create an unwettable surface and result in desiccation of the corneal epithelium. Tear lipocalin (TL), also known as lipocalin-1, is the principal lipid-binding protein in tears. TL has been shown to scavenge lipids from hydrophobic surfaces. The hypothesis that TL can remove contaminating fatty acids and phospholipids from the human corneal surface was tested.

METHODS

TL was purified from pooled human tear samples by size exclusion and ion exchange chromatographies. Tears depleted of TL were reconstituted from fractions eluted by size exclusion chromatography that did not contain TL. Fresh and formalin-fixed human corneas were obtained from exenteration specimens. Fluorescent analogs of either palmitic acid or phosphatidylcholine were applied to the corneal epithelial surface. Tears, TL, or tears depleted of TL were applied over the corneas, and spectrofluorometry and fluorescent stereomicroscopy were used to monitor the removal of fluorescent lipids. Tears used in the experiments were then fractionated by size exclusion chromatography to determine the component of tears associated with fluorescent lipids.

RESULTS

Significant enhancement of fluorescence for 16AP and NBD C(6)-HPC was evident in solutions incubated with whole tears and purified TL but not with tears depleted of TL for fixed and unfixed corneas. After the experiment, size exclusion fractions of tears showed that the fluorescence component coeluted with TL.

CONCLUSIONS

TL scavenges lipids from the human corneal surface and delivers them into the aqueous phase of tears. TL may have an important role in removing lipids from the corneal surface to maintain the wettability and integrity of the ocular surface.

Albumin as a tear supplement in the treatment of severe dry eye

AIM

To determine the efficacy of using albumin tear supplements in the treatment of ocular surface disorders as a substitute for serum eye drops.

METHODS

The effects of albumin on the viability of serum deprived conjunctival cell were observed in vitro. The ability for albumin to compensate for serum was demonstrated by measuring the activity of the apoptosis related enzyme, caspase-3. In an animal study, corneal erosions were inflicted in 40 Japanese white rabbits. Rabbits were treated with 5% or 10% solutions of human albumin, and the decrease in epithelial defect size was compared with saline control and 0.3% sodium hyaluronate. A clinical case series trial of 5% albumin drops was conducted in nine patients with Sjögren's syndrome with severe dry eye.

RESULTS

The addition of albumin to serum deprived conjunctival cells inhibited caspase activity and increased cell viability, showing that albumin can compensate for some of the physiological properties of serum. Corneal erosions in rabbits healed significantly faster (p<0.05) in eyes treated with 10% albumin compared with control and sodium hyaluronate. Patients with Sjögren's syndrome used albumin drops showed statistically significant improvement in fluorescein and rose bengal scores, but not in tear break up time and subjective symptoms. No adverse effects of albumin were observed during the study.

CONCLUSIONS

The use of albumin as a protein supplement in artificial tear solutions is a viable approach in the treatment of ocular surface disorders associated with tear deficiency.

Topical rose bengal: pre-clinical evaluation of pharmacokinetics and safety

BACKGROUND AND OBJECTIVES

Rose bengal (RB) is a potent photosensitizer that has largely been overlooked as a potential photodynamic therapy (PDT) agent. In this study, the feasibility of topical delivery of RB to the epidermis has been evaluated.

STUDY DESIGN/MATERIALS AND METHODS

Topical formulations of RB were assessed on murine and rabbit skin for pharmacokinetic properties, cutaneous toxicity, and photosensitization.

RESULTS

Hydrophilic formulations (<or=1% RB) exhibited rapid, selective, uniform delivery to the epidermis, with no significant acute cutaneous toxicity in normal skin. Illumination (532 nm) elicited no acute phototoxicity for light intensities <or=100 mW/cm(2) at a light dose of 100 J/cm(2); use of higher intensities resulted in superficial thermal damage. Repeat treatment of rabbit skin (weekly for four weeks) elicited minor phototoxicity only at the highest concentration (1% RB).

CONCLUSIONS

These results indicate that RB is safe for PDT treatment of skin disorders, exhibiting negligible effects in normal skin.

Corneal surface changes in keratoconjunctivitis sicca. Part I: The surface proper. A non-contact photomicrographic in vivo study in the human cornea

PURPOSE

To describe corneal surface changes in keratoconjunctivitis sicca (KCS).

METHODS

In all 23 patients with KCS were examined with the slit lamp and photographed by non-contact photomicrography.

RESULTS

Without staining, grey surface cells and small epithelial cysts were visible. Application of fluorescein sodium resulted in two types of micropunctuate (15-30 microm) staining, a nonfluorescent (yellow/brown) and a fluorescent (green) one, in brilliantly green staining of cysts, and in enlarging fluorescent (green) flecks (70-1600 microm) with propensity to confluence. The flecks often developed in inconspicuous areas and showed abnormal subsurface cells. Application of rose bengal resulted in more or less intensively red-stained cells measuring about 30 mm in diameter, often less (15-20 microm), with or without a centrally located nucleus, individual or gathered in small groups or larger patches, and in confluent staining. Smaller and larger cells, with or without nuclei, weakly or strongly stained, were often located close to each other. The smaller green flecks showed a few centrally located red-stained cells, and the larger ones showed many almost uniform small red-stained nucleated ones.

CONCLUSIONS

Corneal epithelial surface disease in the present KCS patients consisted of unspecific features-such as increased light-reflecting property (grey cells), disruptions of intercellular junctions (micropunctuate green fluorescein staining), pathological dye uptake (micropunctuate yellow/brown fluorescein and red rose bengal stainings), and epithelial oedema (microcysts)--and also of features that seemed to be disease specific. Such features were, with fluorescein sodium, focal disruptions of the epithelial barrier function manifesting in enlarging green flecks, and, with rose bengal, abundant nucleated cells, particularly small ones organised in foci. The nature of the abnormal subsurface cells present in the areas of the green flecks, and the mechanisms behind the focal involvement are unclear.

Effect of storage on protein concentration of tear samples

PURPOSE

To determine the effect of storage on protein concentration of tear samples stored at room temperature (RT), 4 degrees C, -20 degrees C and -70 degrees C.

METHODS

Total protein concentration of closed, open (basal tears) and reflex tears (stimulated tears) was measured by modified Bradford's method. SDS-PAGE gel electrophoresis was used to determine the intensity of protein bands. Quantity of various tear proteins was determined by HPLC analysis.

RESULTS

Compared to control samples (0 h) protein concentrations decreased significantly in tear samples stored beyond 4 h (for closed) and 8 h (for open and reflex) at RT. However, no significant change in protein concentrations was observed in closed and reflex tears when stored up to 1 week at 4 degrees C, up to 2 months at -20 degrees C; and up to 4 months at -70 degrees C. Multiple freeze-thaw procedures (6 x per day at 2 h intervals) resulted in 8% decrease (at -20 degrees C) and 10% decrease (at -70 degrees C) of protein concentrations in closed eye tears. SDS-PAGE analysis of tear samples stored at -20 degrees C and -70 degrees C for 4 months greatly affected the intensity of the protein bands. HPLC analysis of tear samples stored at these conditions showed the significant reduction in the peak corresponding to secretory IgA in closed eye tears and a split in the peak corresponding to lysozyme in case of reflex tears.

CONCLUSIONS

Reduction in the total protein concentration, intensity of the protein bands as well as changes in the quantity of tear proteins were observed in the tear samples stored for longer duration of time at various temperatures.

Rose bengal staining and cytologic characteristics associated with lipid tear deficiency

PURPOSE

To characterize ocular surface features of patients with an unstable tear film caused primarily by a lipid tear abnormality resulting from noninflamed meibomian gland dysfunction.

METHODS

Retrospective clinical data and results from rose bengal staining, modified meibography, and impression cytology were reviewed in 78 patients (142 eyes), all of whom had normal tear secretion and clearance verified by the fluorescein clearance test but an unstable tear film evidenced by tear breakup time +/- SD of 3.4 +/- 2.1 seconds (normal, > 8 seconds).

RESULTS

Of 201 symptoms, 147 (73%) were presumably caused by an unstable tear film, 46 (23%) resulted from inflammation, and none were diurnally worsened. All patients had meibomian gland dysfunction characterized by poor or no meibum expression, orifice squamous metaplasia, or acinar atrophy. Rose bengal staining was negative in 95 eyes (67%), positive on nonexposure zones in 30 eyes (21%), and positive on exposure zones in 17 eyes (12%). Among 90 eyes receiving impression cytology, six (7%) were normal, 49 (54%) had pure "lytic" changes characterized by disrupted cell-cell junctions of normal small cells in the nonexposure zone, three (3%) had pure squamous metaplasia without mucous aggregates, two (2%) had squamous metaplasia with mucous aggregates (the latter being a frequent finding of aqueous tear deficiency), and 31 (34%) were mixed with lytic changes and squamous metaplasia.

CONCLUSION

Preferential distribution of rose bengal staining in the nonexposure zone and lytic cytologic changes without squamous metaplasia characterize lipid tear deficiency and help to differentiate it from aqueous tear deficiency in patients with an unstable tear film.