Development of new in vitro models for the study of acne

Abstract

Acne vulgaris is a chronic disease with a high prevalence, not only in teenagers and young adults, but also in adults. It occurs in the pilosebaceous unit, mainly associated with Cutibacterium acnes (C. acnes) hyperproliferation, changes in sebum composition, hyperkeratinization of follicular ducts, leading to inflammation. However, acne's heterogeneity makes it difficult to study, thus there is still a lack of suitable models that can properly replicate, not only the condition’s pathogenesis, but also the intrinsic characteristics of acne. Skin in vitro models arise as useful alternatives to animal testing, providing the scientific research with an important testing tool. They can have different complexity levels, depending on the research’s aim, creating different environments. However, most of them are still very simple, not reflecting the complex interactions present in the skin. In the present work, in vitro models were used to establish different acne conditions, as they are necessary not only to study the mechanisms involved in the disease, but also to analyze the efficacy of different treatments. Aiming to mimic the relationship between C. acnes and the sebaceous glands, bacteria-loaded microparticles were developed, with and without peroxidized squalene. Peroxidized squalene, which is present in sebaceous sites, provides in vitro models the essential lipidic component for C. acnes proliferation. Alginate and collagen microparticles were created and characterized to mimic the encapsulation of the C. acnes in the sebaceous glands. Then, they were inserted in the dermal layer of skin organotypic models, where keratinocytes were added to create an epidermal-like layer, resulting a full-thickness skin in vitro model. As time progressed, microparticles slid out from the models, which was not the desired outcome. However, bacteria and peroxidized squalene still interacted with the models, triggering an immune response and alteration in the skin structure. Nevertheless, to circumvent the microparticles’ limitations, new approaches were tested. Firstly, C. acnes lysate was produced and applied to the epidermal portion of the models to induce an inflammatory response. The lysate was tested at different concentrations for optimization purposes. We observed that the lysate 1:100 concentration was the one with the best outcome to mimic the acne phenotype, since an inflammatory response was triggered and the overall 3D structure of the epidermal layer of the organotypic model was damaged. Additionally, as the sebaceous glands, where usually C. acnes inhabits, are part of the pilosebaceous unit together with the hair follicles, a device to produce hair follicle-like structures was developed. The structures were evident within the models but after stratification, there was not enough space for C. acnes application. In conclusion, we were able to develop functional in vitro skin models, mimicking different severity degrees of the acne disease.

Date of Award	7 Nov 2023
Original language	English
Awarding Institution	Universidade Católica Portuguesa
Supervisor	João Azevedo Silva (Supervisor) & Helena Moreira (Co-Supervisor)