Binding and hydrodynamic properties of muscarinic receptor subtypes solubilized in 3-(3-cholamidopropyl)dimethylammonio-2-hydroxy-1-propanesulfonate

The muscarinic receptor from the cerebral cortex, heart, and lacrimal gland can be solubilized in the zwitterionic detergent 3-(3-cholamidopropyl)dimethylammonio-2-hydroxy-1-propane sulfonate (CHAPSO) with retention of high affinity [3H]N-methyls-copolamine binding. However, in this detergent there are significant differences in the binding properties of the receptors, compared with those observed in membranes and digitonin solution. Some agents retain a degree of selectivity. In the heart and cortex, agonists can bind with high affinity to a receptor-GTP-binding protein complex. A second, lower affinity, agonist binding state is also present, which resembles a class of sites seen in membranes but not in digitonin solution. The high affinity agonist binding state has been resolved from the lower affinity state on sucrose density gradient centrifugation. Hydrodynamic analysis suggests that the high affinity state is approximately 110,000 Da larger than the lower affinity state. The binding properties of the receptor in CHAPSO can be altered to those seen in digitonin by exchanging detergents after CHAPSO solubilization.

Essential fatty acids for dry eye:a review

Purpose Dry eye is a common complaint often encountered in optometric practice. However, it is a difficult condition to treat as clinical signs do not always correlate with patient symptoms. Essential fatty acids (EFA), particularly omega-3 EFA, may be effective in dealing with the underlying causes. Methods A literature review was carried out on the PubMed, ScienceDirect and Ovid databases. Searches included keywords such as ‘dry eye’, ‘essential fatty acids’ and ‘nutrition’ to find articles relating to the treatment of dry eye syndrome (DES) with omega-3 EFAs. Results Omega-3 and -6 EFAs need to be consumed together within a reasonable ratio to be effective. Currently, typical diets in developed countries lack omega-3 EFA and this results in an overexposure to omega-6. Omega-3 supplementation has an anti-inflammatory effect, inhibiting creation of omega-6 prostaglandin precursors. Omega-3 EFAs also demonstrate anti-inflammatory action in the lacrimal gland preventing apoptosis of the secretory epithelial cells. Supplementation clears meibomitis, allowing a thinner, more elastic lipid layer to protect the tear film and cornea. Conclusion Dietary supplementation of omega-3 EFA has already proven to be effective in coronary heart disease and arthritis. Safety is not a concern as it works synergistically with omega-6 in the body. Evidence suggests that supplementation with omega-3 EFA may be beneficial in the treatment and prevention of DES.

Immunoblotting and tear sampling techniques for the study of contact lens-induced variations in tear protein profiles

More information on the biochemical interactions taking place between the tear film and the contact lens is required to further our understanding of the causative mechanisms behind the symptoms of dryness and grittiness often experienced by contact lens wearers. These symptoms can often lead to an intolerance to contact lens wear.

A study of the effects of orally administered female hormones on the volume and composition of lacrimal fluid related to the toleration of corneal contact lenses

This study was designed to evaluate the effects of certain orally active contraceptive steroids on the eye, related to the tolerance of a corneal contact lens. An oestrogen, ethinyloestradiol BP. 0.05 mg, a progestogen, norethisterone acetate BP. 2.50 mg and a control tablet (vitamin C, 50 mg) were utilised. The effect of these preparations on corneal curvature, lacrimal fluid volume and protein composition and directly on corneal lens tolerance was monitored in a group of 23 volunteer patients. The progestogen was found to produce a significant (P≥ 0.05) decrease in tear volume as measured by a 3 minute Schirmer test. A smaller volume reduction was observed with ethinyloestradiol. A normal cornea appears unaffected, within the measurement limits available, by the use of either hormone. However, in the presence of a corneal lens, oestrogen was found to induce substantial corneal steepening, indicative of tissue oedema, during the initial 2-3 weeks of medication. Progestogen occasionally produced a similar effect, which could recur with either hormone shortly after the end of the treatment period. A new method of acrylamide gel electrophoresis was developed for examination of the protein concentration and composition of lacrimal fluid. This allowed much greater resolution of microquantities of unconcentrated fluid than anything previously reported. Quantitation by densitometry has permitted the recording of medication and lens-induced changes in the protein pattern. Tear albumin has been shown to differ from serum albumin and to consist of up to 3 subfractions, 7 further protein fractions may also be resolved. The concentration and probable origin of these proteins have been established and the overall effects of hormone administration described. Individual idiosyncratic responses are also discussed. The study has established tbenature of some effects of contraceptive steroids on the anterior eye, and the probable reasons for resultant corneal lens intolerance.

Tear analysis and lens-tear interactions:part II. Ocular lipids-nature and fate of meibomian gland phospholipids

Purpose: Published data indicate that the polar lipid content of human meibomian gland secretions (MGS) could be anything between 0.5% and 13% of the total lipid. The tear film phospholipid composition has not been studied in great detail and it has been understood that the relative proportions of lipids in MGS would be maintained in the tear film. The purpose of this work was to determine the concentration of phospholipids in the human tear film. Methods: Liquid chromatography mass spectrometry (LCMS) and thin layer chromatography (TLC) were used to determine the concentration of phospholipid in the tear film. Additionally, an Amplex Red phosphatidylcholine-specific phospholipase C (PLC) assay kit was used for determination of the activity of PLC in the tear film. Results: Phospholipids were not detected in any of the tested human tear samples with the low limit of detection being 1.3 µg/mL for TLC and 4 µg/mL for liquid chromatography mass spectrometry. TLC indicated that diacylglycerol (DAG) may be present in the tear film. PLC was in the tear film with an activity determined at approximately 15 mU/mL, equivalent to the removal of head groups from phosphatidylcholine at a rate of approximately 15 µM/min. Conclusions: This work shows that phospholipid was not detected in any of the tested human tear samples (above the lower limits of detection as described) and suggests the presence of DAG in the tear film. DAG is known to be at low concentrations in MGS. These observations indicate that PLC may play a role in modulating the tear film phospholipid concentration.

Randomised masked clinical trial of the MGDRx eyebag for the treatment of meibomian gland dysfunction-related evaporative dry eye

Background/aims To investigate the efficacy and safety of the MGDRx EyeBag (The Eyebag Company, Halifax, UK) eyelid warming device. Methods Twenty-five patients with confirmed meibomian gland dysfunction (MGD)-related evaporative dry eye were enrolled into a randomised, single masked, contralateral clinical trial. Test eyes received a heated device; control eyes a non-heated device for 5 min twice a day for 2 weeks. Efficacy (ocular symptomology, noninvasive break-up time, lipid layer thickness, osmolarity, meibomian gland dropout and function) and safety (visual acuity, corneal topography, conjunctival hyperaemia and staining) measurements were taken at baseline and follow-up. Subsequent patient device usage and ocular comfort was ascertained at 6 months. Results Differences between test and control eyes at baseline were not statistically signi ficant for all measurements ( p>0.05). After 2 weeks, statistically significant improvements occurred in all efficacy measurements in test eyes ( p<0.05). Visual acuity and corneal topography were unaffected (p>0.05). All patients maintained higher ocular comfort after 6 months ( p<0.05), although the bene fit was greater in those who continued usage 1-8 times a month (p<0.001). Conclusions The MGDRx EyeBag is a safe and effective device for the treatment of MGD-related evaporative dry eye. Subjective benefit lasts at least 6 months, aided by occasional retreatment. Trial registration number NCT01870180.

Microwave decontamination of eyelid warming devices for the treatment of meibomian gland dysfunction

PURPOSE: The role of bacteria in meibomian gland dysfunction is unclear, yet contamination of compresses used as treatment may exacerbate this condition. This study therefore determined the effect of heating on bacteria on two forms of compress. METHODS: Cotton flannels and MGDRx EyeBags (eyebags) were inoculated by adding experimental inoculum (Staphylococcus aureus, Streptococcus pyogenes, Pseudomonas aeruginosa; one species for each set of 3 eyebags and flannels). One of each were then randomised in to 3 groups: no heating (control); therapeutic (47.4±0.7°C); or sanitisation (68±1.1°C). After treatment, bacteria cell numbers were calculated. The experiment was repeated in triplicate. RESULTS: There was a statistically significant difference between each treatment with the eyebag for S. aureus (control=7.15±0.11logC/ml, therapeutic heating=5.24±0.59logC/ml, sanitisation heating=3.48±1.43logC/ml; P<0.001) and S. pyogenes (7.36±0.13, 5.73±0.26, 4.75±0.54; P<0.001). P. aeruginosa also showed a significant reduction (P<0.001) from control (6.39±0.34) to therapeutic (0.33±0.26) and sanitisation (0.33±0.21), but the latter were similar (P=1.000). For the flannels, there was significant difference between each treatment for S. aureus (6.89±0.46, 3.96±1.76, 0.42±0.90; P<0.001). For S. pyogenes, there was a significant reduction (P<0.001) from control (7.51±0.10) to therapeutic (5.91±0.62) and sanitisation (5.18±0.8), but the latter were similar (P=0.07). For P. aeruginosa, there was a significant difference (P<0.001) from control (7.15±0.36) to sanitisation (5.83±0.44); but not to therapeutic (6.84±0.31) temperatures (P=0.07). CONCLUSIONS: Therapeutic heating produces a significant reduction in bacteria on the eyebags, but only sanitisation heating appears effective for flannels. However, patients should be advised to heat the eyebag to sanitisation temperatures on initial use.