Components Of Tear Fluid Research Articles

Normal and Sjogren’s syndrome models of the murine lacrimal gland studied at single-cell resolution

The lacrimal gland is of central interest in ophthalmology both as the source of the aqueous component of tear fluid and as the site of autoimmune pathology in the context of Sjogren's syndrome (SjS). To provide a foundational description of mouse lacrimal gland cell types and their patterns of gene expression, we have analyzed single-cell transcriptomes from wild-type (Balb/c) mice and from two genetically based SjS models, MRL/lpr and NOD (nonobese diabetic).H2b, and defined the localization of multiple cell-type-specific protein and mRNA markers. This analysis has uncovered a previously undescribed cell type, Car6+ cells, which are located at the junction of the acini and the connecting ducts. More than a dozen secreted polypeptides that are likely to be components of tear fluid are expressed by acinar cells and show pronounced sex differences in expression. Additional examples of gene expression heterogeneity within a single cell type were identified, including a gradient of Claudin4 along the length of the ductal system and cell-to-cell heterogeneity in transcription factor expression within acinar and myoepithelial cells. The patterns of expression of channels, transporters, and pumps in acinar, Car6+, and ductal cells make strong predictions regarding the mechanisms of water and electrolyte secretion. In MRL/lpr and NOD.H2b lacrimal glands, distinctive changes in parenchymal gene expression and in immune cell subsets reveal widespread interferon responses, a T cell-dominated infiltrate in the MRL/lpr model, and a mixed B cell and T cell infiltrate in the NOD.H2b model.

Urea transporter-B expression on the ocular surface and in the lacrimal glands

ObjectiveUrea is a component of tear fluid showing a significantly decreased concentration in dry eye disease. The urea content of tear fluid may depend on urea transporters. The purpose of this study was to examine the expression of urea transporter B (UT-B) at the ocular surface and in the lacrimal glands. MethodsUT-B protein and mRNA expression was investigated in human, porcine, and murine samples. Immunohistochemical staining for UT-B was performed on paraffin sections of human, porcine, and murine corneas, eyelids, and lacrimal glands (n = 5 each). Reverse transcriptase polymerase chain reaction was conducted to detect UT-B mRNA in human and murine cornea, conjunctiva, Meibomian gland, and lacrimal gland (n = 5 each). ResultsUT-B protein expression was comparable in all three species. It was found in the corneal epithelium and endothelium, in the conjunctival epithelium, in the end pieces and excretory ducts of the lacrimal gland, Meibomian gland, and in the glands of Moll and Zeis. The glands of Zeis and the Meibomian glands showed intense UT-B signals in the basal layers of the alveolar epithelia and in the cells of the ductal epithelia. UT-B mRNA was detected in all samples analyzed. ConclusionUT-B is expressed by the cells and tissues of the ocular surface and in the lacrimal glands. Potential changes in urea transporter expression might have implications for the pathogenesis of dry eye disease. Since comparable results were obtained for all species investigated, the presented findings may open the door for DED-relevant experimentation on porcine and murine model systems.

Tear fluid biomarkers in major depressive disorder: Potential of spectral methods in biomarker discovery

Spectroscopic methods represent a group of analytical methods that demonstrate high potential in providing clinically relevant diagnostic information, such as biochemical, functional or structural changes of macromolecular complexes that might occur due to pathological processes or therapeutic intervention. Although application of these methods in the field of psychiatric research is still relatively recent, the preliminary results show that they have the capacity to detect subtle neurobiological abnormalities in major depressive disorder (MDD). Methods of mass spectrometry (MALDI-TOF MS), zymography, synchronous fluorescence spectroscopy (SFS), circular dichroism (CD) spectroscopy, Fourier-transform infrared (FTIR) spectroscopy and atomic force microscopy (AFM) were used to analyze the human tear fluid of subjects with MDD. Using MALDI-TOF MS, two diagnostically significant peaks (3747 and 16 411 m/z) were identified with an AUC value of 0.89 and 0.92 in tear fluid of subjects with MDD vs controls, respectively. We also identified various forms of matrix metalloproteinase 9 in subjects with MDD using zymography and synchronous fluorescence spectra (SFS) showed a significant increase in fluorescence intensity at 280 nm. CD spectra were redshifted in tear fluid of subjects with MDD vs healthy controls. FTIR spectroscopy showed changes in the positions of peaks for amide A, I, II in tear fluid of subjects with MDD vs controls. Moreover, atomic force microscopy (AFM) showed different pattern in the crystal structures of tear fluid components in subjects with MDD. SFS, CD, FTIR spectroscopy, AFM and MALDI-TOF MS confirmed, that the human tear fluid proteome could be helpful in discriminating between the group of subjects with MDD and healthy controls. These preliminary findings suggest that spectral methods could represent a useful tool in clinical psychiatry, especially in establishing differential diagnosis, monitoring illness progression and the effect of psychiatric treatment.

Tear protein analysis in patients with primary acquired nasolacrimal duct obstruction treated with lacrimal passage intubation.

The pathophysiology of nasolacrimal duct obstruction (NLDO) may involve quantitative as well as qualitative changes in tears. We measured tear protein concentrations in patients with primary acquired NLDO and compared them with the tear proteins in healthy individuals and patients with dry eye disease. Case-control study. Twenty-four patients diagnosed with primary acquired NLDO who underwent endoscopic lacrimal passage intubation were included in the study. Tear fluid was collected with Schirmer's test strips three times: before intubation, after intubation while the nasolacrimal tube was in place, and after extubation. At the same time, 24 age-matched normal controls and 24 patients with dry eye were selected from subjects whose tears were collected during the same study period. We measured the following components of tear fluid: total protein, lactoferrin, albumin, and interleukin 6 (IL-6) levels. Total proteins and albumin levels in tears of the NLDO group were significantly lower than those of the control group (P < 0.001 and P = 0.014, respectively, Mann-Whitney U test). Total proteins, albumin, and lactoferrin levels were significantly increased after extubation of nasolacrimal tube (P < 0.001, P = 0.004, and P = 0.029, respectively, Wilcoxon matched-pairs signed-rank test). There were no statistically significant differences in total protein, albumin, lactoferrin and IL-6 levels between patients with NLDO after lacrimal passage extubation and controls. Our study shows distinct differences in protein composition of tear fluid in NLDO eyes and demonstrates that these can be normalized by nasolacrimal tube placement.

Short-Term Reproducibility of MUC5AC Measurement in Human Tear Fluid.

The assessment of tear fluid components is a common and valuable approach to understanding ocular surface disease and testing the efficacy of novel therapeutic strategies. However, the interpretation and utility of the findings can be limited by changes in the composition of the tear film, particularly in studies requiring repetitive patient sampling. Here, tear samples were collected twice within a one-hour interval to evaluate the short-term reproducibility of an immunoassay aimed to measure the amount of MUC5AC mucin. We found no statistical difference in total protein or MUC5AC content between the two consecutive collections of tear fluid, although the inter-individual variability in each group was high, with coefficients of variation exceeding 30% and 50%, respectively. Scatterplots showed a significant correlation in both protein and MUC5AC following collection within a one-hour interval. These data indicate that, regardless of the high inter-individual variability, repeated collection of tear fluid within an hour interval produces reproducible intra-individual data in terms of MUC5AC mucin content, and suggest that the normal mucin composition of the tear fluid can be re-established within an hour of the initial collection.

Chitosan surface modified hydrogel as a therapeutic contact lens

Therapeutic contact lenses have attracted significant attention during the last decades. In this study, we used chitosan‐conjugated poly(2‐hydroxyethyl methacrylate) (PHEMA) for contact lens application. We aimed to increase affinity of anionic drugs, which are used in treatment of eye diseases. In this regard, we evaluated delivery of the small molecule anionic drug, ascorbic acid from the chitosan‐conjugated PHEMA. Chitosan immobilization improves drug loading efficiency and induces sustained release of ascorbic acid. The chitosan modified hydrogel also reduces the biofouling of tear fluid components. Our results showed that surface modification by chitosan inhibits protein and bacterial deposition on the contact lens. Protein absorption analysis revealed that neat PHEMA adsorbed tear proteins at a density of 28.4 ± 4.4 μg/cm2, whereas the chitosan‐conjugated hydrogel adsorbed tear proteins at a density of 18.5 ± 1.8 μg/cm2. Moreover, the neat PHEMA bacterial adhesion had a mean CFU value of 273 ± 27. However, a significant decrease in the number of bacterial colonies was observed in the chitosan group with a CFU value of 9 ± 6.

The importance of fine dust for the development of an environmentally induced dry eye

Abstract Purpose Environmental conditions promote dry eye by destruction of tear fluid and induction of cell damage. Fine dust is not only present in an urban polluted environment, but also in a cigarette fume or candle light dust loaded home environment. We wanted to determine, if fine dust affects the tear fluid components and conjunctival cells. Methods Human tear fluid from volunteers was obtained and incubated with fine dust suspensions. Possible tear protein changes were analysed by polyacrylamidegel‐electrophoresis (PAGE). Cultivated human conjunctival cells (CHANG‐cells) were incubated with fine dust suspensions as well as exposed to ultraviolet light (UV‐A). Cytomorphological changes and cell vitality were analysed via CASY1 Cell Counter and MTS‐assay. Results Fine dust suspensions destroy tear fluid proteins, particularly in combination with UV‐A‐light irradiation. Moreover, the incubation of human conjunctival cells with fine dust suspensions leads to a statistically significant decrease of cell vitality, depending on the fine dust concentration and incubation period. Additional UV‐A‐irradiation induces a further reduction of cell vitality. Conclusion Due to the alterations of human tear proteins and conjunctival cells caused by fine dust and exaggerated by UV‐A‐irradiation, fine dust can also be responsible for the development of an environmentally induced dry eye.

Expression Profile of Aquaporins in Human Nasolacrimal Duct Epithelium

Purpose: To determine whether the epithelium of the human nasolacrimal ducts contains aquaporins (AQPs), a family of membrane proteins that function as selective pores and are able to transport water, glycerol, and other small solutes across the cell plasma membrane.Methods: Expression of AQPs 0 and 1–10 in human nasolacrimal duct tissue was determined by reverse transcription polymerase chain reaction (RT-PCR). Positive PCR amplification products were verified by direct cDNA sequencing. Western blot analysis was used to detect AQPs 3–5. Antisera specific for AQPs were used in immunohistochemical analysis to determine the presence and distribution of ten AQPs (AQP 0 and 1–9) in epithelia and subepithelial glands of the nasolacrimal ducts. All samples investigated originated from human postmortem tissue.Results: In human nasolacrimal duct samples, AQPs 1, 3, 4, 5, 7, 8, 9, and 10 were identified by RT-PCR. No RT-PCR products were detected for AQPs 0, 2, and 6. All AQPs, which were detected by RT-PCR, were also confirmed by direct sequencing of the cDNA. Immunohistochemical analyses revealed AQPs 1, 3, 5, 7, 8, and 9 in human nasolacrimal duct epithelium and were detected in different cells. Expression of AQP 4 could not be detected immunohistochemically but by Western blot analysis. Protein detection of AQP 10 could not be performed due to the unavailability of an appropriate antibody.Conclusions: The results suggest specific roles for AQPs in water transport through the epithelium of the nasolacrimal ducts and underline the presumption that tear fluid components are selectively absorbed in the nasolacrimal passage.

Anatomie und Physiologie der ableitenden Tränenwege

The human nasolacrimal ducts consist of the upper and lower lacrimal canaliculi, the lacrimal sac and the nasolacrimal duct and drain tear fluid from the ocular surface into the nose. The lining epithelium of the lacrimal sac and the nasolacrimal duct is lined by microvilli supporting the hypothesis that tear fluid components are absorbed. Based on its composition epithelial secretions fulfill functions in tear transport and antimicrobial defense. Further defense mechanisms are displayed by IgA and defense cells which show a special intraepithelial and subepithelial distribution. Moreover, tear duct-associated lymphoid tissue (TALT) is present, displaying the cytomorphological and immunophenotypic features of mucosa-associated lymphoid tissue (MALT). The mechanisms of tear outflow are not yet resolved and several hypotheses exist. Significance is attributed to the lacrimal part of the orbicularis eye muscle surrounding the canaliculi, the helically arranged system of connective tissue fibres and the cavernous body that surrounds the lacrimal sac and the nasolacrimal duct. Moreover, the cavernous body has a function in protecting the lacrimal passage and is active during emotions.

Dynamics of tear fluid components transportation through contact lenses

The interference optical method has been applied to monitor the transportation of Na + and Cl − in solution through new and used contact lenses. The phenomenon of passive transportation (simple diffusion), induced by differences in osmotic pressure on both sides of the contact lenses has been discussed. Permeability coefficient of contact lenses of different optical power: −2.75 D and −3.75 D has been calculated.

Iodide protection from UVB irradiation-induced degradation of hyaluronate and against UVB-damage of human conjunctival fibroblasts

To determine whether iodide protects from UVB irradiation-induced destruction of hyaluronate and against UVB injury of cultured human conjunctival fibroblasts. Hyaluronate and primary cultured human conjunctival fibroblasts were incubated with various concentrations of iodide and then exposed to UV light irradiation of 312 nm. Hyaluronate destruction was determined by viscosity measurements. Cell viability was assessed with MTT assay. Iodide protects hyaluronate from UVB light-induced degradation of this macromolecule in a concentration-dependent manner. Incubation of human conjunctival fibroblasts with iodide inhibited cells from damage by UVB light. Iodide protects hyaluronate, a component of tear fluid and tissues of the anterior part of the eye, against UVB light-induced degradation. Also, injury of human conjunctival cells can be prevented by incubation with iodide before UVB irradiation. The mechanism of protection is likely to include an antioxidative reaction. To support the natural defence mechanisms of the eyes, the administration of an antioxidant such as iodide to artificial tears, for example, may help to prevent the damage of the eye provoked by oxidative stress.

Drainage of Tears: Impact on the Ocular Surface and Lacrimal System

The human efferent tear ducts are part of the lacrimal system. Because little knowledge exists concerning the physiology of the nasolacrimal system, and hence its pathophysiology, the nasolacrimal system has received almost no consideration as a possible factor in dry eye. The human nasolacrimal ducts consist of the upper and the lower lacrimal canaliculus, the lacrimal sac, and the nasolacrimal duct. As a draining and secretory system, the efferent tear ducts play a role in tear transport and nonspecific immune defense. Moreover, components of tear fluid are absorbed in the nasolacrimal passage and are transported into a surrounding vascular system. This system is similar to a cavernous body that is subject to autonomic control and regulates tear outflow. Tear duct-associated lymphoid tissue (TALT) is present in the efferent tear ducts, displaying the cytomorphological and immunophenotypic features of mucosa-associated lymphoid tissue (MALT). Under normal conditions, tear fluid components are constantly absorbed into the blood vessels of the surrounding cavernous body. These vessels are connected to the blood vessels of the outer eye and could act as a feedback signal for tear fluid production, which ceases if these tear components are not absorbed. In this way, dry eye could be initiated. Defective stimulation of TALT could result in abnormal immune deviation at the ocular surface, leading to an autoimmunological response that causes dry eye pathology.

Plasminogen activator activity and inhibition in rabbit tears after photorefractive keratectomy

Plasminogen activator is a normal component of tear fluid that plays a role in corneal wound healing processes. This work examines whether inhibitor-induced low levels of plasminogen activator activity (PAA) during corneal re-epithelialization after excimer laser photorefractive keratectomy (PRK) correlates with the eventual occurrence of haze in rabbit eyes. Tear samples were collected with glass capillaries from 16 eyes of eight New Zealand rabbits, using i.m. injection of pilocarpine hydrochloride for stimulation. Tears were collected before and after PRK surgery, and then daily for 5 days, and every fourth day thereafter for 3 months. Both eyes underwent PRK treatment. One eye of each rabbit was treated as a control while the contralateral eye was treated with aprotinin, a serine protease inhibitor, over the first 7 days. PAA in the tear samples was measured by a spectrophotometric method using human plasminogen and chromogenic peptide substrate S-2251. For the eight control eyes after PRK, the PAA values were significantly lower (day 1) and higher (days 2 and 3) than the equilibrium PAA ( p<0·001). The corneas remained clear in each of these control eyes. For the eight contralateral aprotinin-treated eyes after PRK, the PAA values on days 1–7 were significantly lower than the equilibrium PAA (p<0·001). All eight of these aprotinin-treated eyes developed corneal haze after 2 months. There was no significant difference ( p=0·06) between control and aprotinin-treated eyes for the equilibrium PAA after 19 days. We conclude that a corneal wound healing abnormality (haze) develops in rabbit eyes after PRK when PAA levels are reduced using aprotinin for a week following PRK.

The effect of sample treatment on separation profiles of tear fluid proteins: qualitative and semi-quantitative protein determination by an automated analysis system.

Qualitative and quantitative determination of tear fluid components is of increasing interest in ophthalmology. Until now, for diagnosis and course control of some diseases of the anterior parts of the eye, different methods for tear fluid protein analysis are available. Results can be obtained by polyacrylamide gel electrophoresis (PAGE), immunochemistry, and high-performance liquid chromatography (HPLC). A new method for protein separation, identification and semi-quantitative determination on a chip-based micro-fluidic technique is used for the first time to investigate tear fluids. Normal human reflex tears were obtained by stimulation with China mint oil and collected using glass capillary tubes. A lab-on-a-chip technology (developed by Agilent Technologies, Waldbronn, Germany, in co-operation with Caliper Technologies, Mountain View, California, USA) was used for separation and semi-quantitative determination of tear proteins. Tear fluid was separated on the Agilent 2100 Bioanalyzer in combination with the Protein 200 LabChip kit and the dedicated protein assay software. Time and temperature of the incubation with sample buffer were varied, and the influence of these parameters on protein separation profiles was studied. Tear proteins were also analysed by PAGE, and the results obtained by both methods were compared. The different proteins of tear fluid can be separated by the Agilent 2100 Bioanalyzer method in very short time. By this method, the molecular weight as well as the concentration of proteins can be determined. Data are automatically stored in digital format and can be retrieved and shared. Results of this technology were comparable with the protein pattern obtained by PAGE. It was confirmed by both methods that, depending on incubation time of tear fluid with sample buffer and on temperature, different protein pattern can be obtained from the tears of one specimen. Tear proteins - in contrast to serum or aqueous humour proteins - are very sensitive to changes in sample buffer temperature as well as incubation time with buffer. To obtain comparable results for tear fluid proteins, the sample buffer applied and the incubation time and temperature must be observed carefully. This can be demonstrated by both the new Agilent 2100 Bioanalyzer method and PAGE. These results are of importance when comparing tear fluid protein pattern for the diagnosis and course control of dry-eye syndrome and of other diseases of the anterior part of the eye.

Nasolacrimal ducts and the dry eye

The knowledge regarding the pathogenesis, diagnosis, and treatment of dry eye has made large advances in recent years. However, many questions are still unanswered. Although the nasolacrimal ducts are part of the tear system they have been paid nearly no attention regarding dry eye. The present knowledge about the nasolacrimal ducts is presented and discussed in a context with dry eye. A PubMED search was conducted for articles published from 1966 to the present; in addition, review articles as well as book chapters were considered and discussions with investigators in the field were performed. As a draining and secretory system, the nasolacrimal ducts play a role in tear transport and non-specific immune defense. Moreover, components of tear fluid are absorbed in the nasolacrimal passage and are transported into a vascular system that surrounds the nasolacrimal sac and nasolacrimal duct. This system is comparable to a cavernous body and it is connected to the blood vessels of the outer eye. Also it is subject to vegetative control. Organized mucosa-associated lymphoid tissue (MALT) is present in the nasolacrimal ducts displaying the cytomorphological and immunophenotypic features of MALT. The normally constant absorption of tear fluid components into the blood vessels of the surrounding cavernous body that are connected to the blood vessels of the outer eye, could be a feedback signal for tear fluid production, which comes to a halt if these tear components are not absorbed. Thus, dry eye could be initiated. Defective stimulation of tear duct-associated lymphoid tissue (TALT) could result in abnormal immune deviation at the ocular surface leading to an autoimmunological response that causes dry eye pathology.

The effect of nasal mucosal stimulation on Schirmer tests in Sjögren's syndrome and dry eye patients.

The Schirmer test evaluates tear quantity and reflects the aqueous component of tear fluid. This test distinguishes dry eye patients, including patients with Sjogren’s syndrome (SS), from normal subjects. It is difficult, however, to differentiate patients without SS (non-SS) from patients with SS using this test only. Tsubota reported the importance of the Schirmer test with nasal stimulation and noted the test was useful to determine the reserve function for aqueous tear production.

Platelet-derived growth factor-BB (PDGF-BB) in tear fluid: a potential modulator of corneal wound healing following photorefractive keratectomy

PURPOSE. To measure the pre- and postoperative tear fluid platelet-derived growth factor-BB (PDGF-BB) concentrations of patients undergoing excimer laser photorefractive keratectomy (PRK). METHODS. Tear fluid samples from PRK patients were collected with scaled microcapillary tubes preoperatively (Day 0, N = 23), on the second (Day 2, N = 24) and on the seventh (Day 7, N = 14) postoperative days. The PDGF-BB concentration was measured using a sandwich enzyme immunoassay, and the PDGF-BB release was calculated by multiplying the concentration by the tear fluid flow in the collection capillary. RESULTS. The mean tear fluid flow in the capillary was 17.4 µl/min (range 1.4–55.0) on Day 0, 62.6 µl/min (4.3–125.0, p = 0.0000) on Day 2, and 15.5 µl/min (1.2–50.0, NS) on Day 7. Seventeen percent (4/23) of the Day 0 samples contained detectable concentrations of PDGF-BB (range 95–1330 ng/l). On Day 2 all (24/24) tear samples showed significantly increased concentrations (mean 507 ng/l, range 45–2280 ng, p = 0.0001) and releases (mean 27.6 pg/min, range 1.0–98.0; p = 0.0000). On Day 7 PDGF-BB was still measurable in 9/14 samples (mean concentration 194 ng/l, range < 5–925 ng/l, and mean release 1.9 pg/min, range 0.04–6.8 pg/min). CONCLUSIONS. PDGF-BB is an inducible component of tear fluid. In spite of hypersecretion caused by the corneal wound, PDGF-BB concentrations raised significantly during the initial wound healing. Increased PDGF-BB release during the two postoperative days following PRK suggests a role in corneal wound healing.

Analysis of Human Tear Fluid Components, Inhibiting Protein Adhesion to Plastic Surfaces

In a previous paper we reported the presence of components in human tear fluid that block the interaction of proteins with plastic surfaces, interfering with tear protein ELISA and proposed the term coating inhibiting activity. The purpose of the study presented here was to further analyse these components. Coating inhibitory activity in human reflex tears was analysed by lectin affinity chromatography, using the agarose bound lectin Artocarpus integrifolia agglutinin (Jacalin), gel filtration, sodium dodecyl sulfate–polyacrylamide gel electrophoresis (SDS–PAGE), blotting and Jacalin staining. For coating inhibitory activity assay in experimental tear samples, the binding of the protein Avidin-conjugated horseradish peroxidase to the polystyrene surface of ELISA micro-titer plate wells, preincubated with the experimental tear samples was measured. In addition, tears were incubated with scrapings of the ELISA plates used in the assay and with six different types of contact lenses (two rigid gas permeable and four hydrogel soft contact lenses) for analysis of adsorbed components. Lectin affinity chromatography of tears yielded a Jacalin-binding and a non-Jacalin-binding preparation, both exhibiting coating inhibitory activity but representing chemically different preparations as observed by SDS–PAGE. After performing gel filtration, coating inhibitory activity eluted with similar retention in both preparations. In fractions exhibiting activity, tear proteins of low molecular weight (< 40 kDa) were detected. Among these, two Jacalin-binding glycoproteins were detected; a major component of approximately 28 kDa and a somewhat smaller minor component. All low molecular weight components were also detected on the scrapings, incubated with tears. The possibility that coating inhibitory activity in tears might reside in a component of larger molecular size can however not be excluded. The human tear proteins secretory Immunoglobulin A, lactoferrin and lysozyme are not involved in coating inhibition. On one of the two rigid gas permeable contact lenses incubated with the tears, the 28 kDa glycoprotein was detected. From the data obtained in our study we conclude that coating inhibitory activity in tears seems to be associated with multiple components of low molecular weight.

Basic fibroblast growth factor in human tear fluid: detection of another growth factor.

Topical application of various growth factors have shown promising experimental data in speeding up corneal wound healing. Similar effects have been reported for another group of proteins, fibroblast growth factors (FGFs). One of them, basic FGF (bFGF), stimulates the proliferation of cells of mesodermal as well as of neuroectodermal origin and is highly angiogenic. The aim of the present study was to investigate the presence of bFGF in human tear fluid. After establishing an advanced enzyme-linked immunosorbent assay technique, tear fluid was collected from 15 healthy individuals before and after stimulation of reflex tearing. In none of the tear fluid samples collected prior to induction of reflex tearing could FGF be detected. Of the 15 samples collected during reflex tearing, six (40%) contained measurable amounts of bFGF. The amount of bFGF appeared to decrease with increasing tear fluid flow, suggesting a dilution effect. This study gives strong evidence that bFGF, as previously shown for epidermal growth factor and transforming growth factor-alpha, may occur in human tear fluid of healthy individuals after induction of reflex tearing and, in very low concentrations, under normal conditions. Whether bFGF can to be considered a constant component of tear fluid, however, remains to be investigated.

Transforming growth factor-alpha is a constant component of human tear fluid.

Growth factors are known as a family of polypeptides with powerful influences on angiogenesis, tumor growth and wound healing. Transforming growth factor-alpha (TGF-alpha) and epidermal growth factor (EGF) are structurally related peptides which bind to the same receptor, EGF-R, and also exert similar effects. EGF is a natural component of human tears, and ocular disease leads to decreased concentrations in tear fluid. Using a sensitive radioimmunoassay we investigated whether TGF-alpha is also to be considered a natural component of tear fluid and in which concentrations it occurs. All of 46 tear fluid samples from 24 volunteers contained TGF-alpha. The mean concentration was 161.4 pg TGF-alpha/ml (SD 11.6 pg). No statistically significant correlation was found between tear fluid flow and TGF-alpha concentration in the sample. However, the concentration of TGF-alpha in tear fluid decreased significantly with increasing total time of tear fluid collection (P = 0.002). TGF-alpha levels in samples collected from males (n = 16) appeared to be higher (mean 247.0 pg/ml, SD 15.3 pg/ml) than in those from females (n = 30; mean 180.0 pg/ml, SD 8.5 pg/ml; P = 0.05). No correlation was found between the age of the individuals and the concentration of TGF-alpha in their tear fluid. The findings show that TGF-alpha is, like EGF, a constant component of human tear fluid. The dependence of TGF-alpha concentration on tear fluid flow and the physiological importance of its presence for corneal integrity and ocular surface physiology, however, require further investigation.