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Bioactive lipids at the ocular surface: from Langmuir surface balance to ophthalmic nanoemulsions

Periodic Reporting for period 1 - BioNanoLip (Bioactive lipids at the ocular surface: from Langmuir surface balance to ophthalmic nanoemulsions)

Período documentado: 2020-01-06 hasta 2022-01-05

The tear film lipid layer (TFLL) is a microscopically thin film of oils that is key to preventing the tear film from evaporating. Dry eye disease develops when this lipid layer malfunctions and affects up to 30% of the human population across the globe. Mixing ophthalmic nanoemulsions with the tear film lipid layer, which has an exceptionally slow turnover rate, could lead to improved treatments for dry eye disease as well as for glaucoma, a major vision-threatening disease. The BioNanoLip project aims to increase our understanding of lipid layer functionality and dry eye disease mechanisms. It also explores molecules and formulations that can enhance lipid layer functionality and lead to new therapies.
In the course of the action meibomian and tear layers were studied with diverse range of mutually complimentary techniques and approaches: Langmuir surface balance, Brewster angle microscopy, fluorescence microscopy and spectroscopy, in situ and in vivo model systems. Thus it was possible to characterize (i) the dynamic interfacial properties and structure of the meibomian and tear film at natural and model air/tear surface, (ii) to elucidate the contribution of the individual lipid, tear and pharmaceutical molecules to the performance of the layers in vitro and in vivo and (iii) to probe the correlation between the structure and the dynamic interfacial properties of the films.
The major conclusions reached are:

- There is significant correlation between the surface properties of meibomian and tear films and the (in)stability of human tear film in vivo at the ocular surface

- The structural heterogeneity of the meibomian and tear lipid films in vitro correlates with the heterogeneity of the tear film lipid layer (TFLL) at the air/tear surface in vivo.

- Zwitterionic phospholipids (PL) cannot be considered as magic molecules for the supplementation of meibomian (MGS) films. In contrast PL tended to disrupt the interfacial structure and properties of the films. This can be explained with the higher surface activity of PL (as compared to MGS) which suppresses the normal spreading and functionality of TFLL and aligns with recent reports that increased content of PL is a pathological feature related to inflammation. Anionic phospholipids (APL) as well as partially ionized lipids like O-Acyl-ω-hydroxy Fatty Acids (OAHFA) were able to partially recover the viscoelasticity of MGS films but had moderate capability to enhance the surface structure of MGS layers.

- Non-lipidic polymers (endogenous for the human tears) were particularly efficient to enhance the surface structure and properties of MGS and tear lipid films both in vitro and in vivo. Particularly efficient were cationic lacritin peptides (lacritin is the sole protein found to be down regulated in dry eye) as well as high molecular weight mucomimetic polymers. The latter finding suggests that secretory tear mucin MUC5AC as well as MUC5AC-like polymers may serve as “bridge” molecules that synchronize the performance of the lipid and aqueous soluble components of human tears.

- The ratio between the major non-polar lipids in MGS, wax and sterol esters, is important for the viscoelasticity of MGS layers and correlates with MGS phase transitions. The latter agrees with recent lipidomic studies showing that it might be the nonpolar lipid profile of MGS that degrades in dry eye.

- Pharmaceutically applicable cationic lipid, cetalkonium chloride (CKC), developed by Santen SAS in combination with other molecules proved to be beneficial for the performance of tear film lipid layer (and tear film as a whole), both in vitro and in vivo

Apart from five international publications in high ranked reputable journals, the results obtained in the grant serve also as a base for further project proposals for international funding currently co-prepared by Georgi:

- A project application “Lacritin-OAHFA relationships at surfaces or why Lacritin and OAHFA matter for the tear film” by Professor Gordon Laurie, University of Virginia, Georgi Georgiev and Manuel Prieto for researcher initiated RO1 grant to be submitted June 2022 to National Institute of Health, USA. The grant aims to attract funding from USA to EU universities, i.e. University of Lisbon and Sofia University.

- A project application “OCUBIO – Ocular Biomarkers for personalized detection of autoimmunity” with Centre Hospitalier National d'Ophtalmologie des Quinze-Vingts (Paris) and Santen SAS is in ongoing preparation phase to be submitted to H2022. The project consortium is led by Prof. Christophe Baudouin who became acquainted with the Action results in a special conference event organized by Santen SAS in December 2021 in Paris at Centre Hospitalier National d'Ophtalmologie des Quinze-Vingts (Paris).

Further applications to Portuguese and extramural science funding agencies are under consideration.
The results have the potential to result both in (i) development of novel methods for diagnostics of dry eye based on evaluation of tear film lipid layer heterogeneity in vivo and (ii) identification of novel tools and novel directions to look for molecules for the treatment of dry eye. The identification of the strong impact of non-lipidic molecules (lacritin peptides, mucomimetic polymers) on the properties of MGS and tear lipids reveals novel aspects on the mechanism of dry eye disease and may play major role for development of better diagnostics and therapies. Currently a strategy is discussed with Santen SAS and clinical and industry experts on how to enhance the awareness of the ophthalmic community about the rheological properties and structural stability of TFLL for the development of Dry Eye and to include these parameters as endpoints for the diagnostic and therapy of dry eye by the European Medical Agency.
The products, developed by Santen SAS, an innovation oriented pharmaceutical SME company, gained a strong knowledge based scientific base and will contribute for the competitiveness of the European pharmaceutical industry.
Within IST, Lisbon, a consideration is ongoing about the opportunity to claim intellectual property rights about the implementation of lipid coated droplets, a band new approach to tear biophysics, as a useful model to probe the interactions of ophthalmic nanoemulsions with tear fluids.
Overall, the new knowledge regarding both fundamental science, and also pharmaceutical products for Santen SAS, the ongoing preparation of high profile project applications, as well as connections with leading international experts, will increase the competitiveness of the EU science and industry.
Tear film lipids in health and disease, at surfaces and in bulk tears