Modeling the effects of hyaluronic acid degradation on the regulation of human astrocyte phenotype using multicomponent interpenetrating polymer networks (mIPNs)

Fabrication and Characterization of Quad-Component Bioinspired Hydrogels to Model Elevated Fibrin Levels in Central Nervous Tissue Scaffolds

Multicomponent interpenetrating polymer network (mIPN) hydrogels are promising tissue-engineering scaffolds that could closely resemble key characteristics of native tissues. The mechanical and biochemical properties of mIPNs can be finely controlled to mimic key features of target cellular microenvironments, regulating cell-matrix interactions. In this work, we fabricated hydrogels made of collagen type I (Col I), fibrin, hyaluronic acid (HA), and poly (ethylene glycol) diacrylate (PEGDA) using a network-by-network fabrication approach. With these mIPNs, we aimed to develop a biomaterial platform that supports the in vitro culture of human astrocytes and potentially serves to assess the effects of the abnormal deposition of fibrin in cortex tissue and simulate key aspects in the progression of neuroinflammation typically found in human pathologies such as Alzheimer's disease (AD), Parkinson's disease (PD), and tissue trauma. Our resulting hydrogels closely resembled the complex modulus of AD human brain cortex tissue (~7.35 kPa), promoting cell spreading while allowing for the modulation of fibrin and hyaluronic acid levels. The individual networks and their microarchitecture were evaluated using confocal laser scanning microscopy (CLSM) and scanning electron microscopy (SEM). Human astrocytes were encapsulated in mIPNs, and negligible cytotoxicity was observed 24 h after the cell encapsulation.

Out of the core: the impact of focal ischemia in regions beyond the penumbra

The changes in the necrotic core and the penumbra following induction of focal ischemia have been the focus of attention for some time. However, evidence shows, that ischemic injury is not confined to the primarily affected structures and may influence the remote areas as well. Yet many studies fail to probe into the structures beyond the penumbra, and possibly do not even find any significant results due to their short-term design, as secondary damage occurs later. This slower reaction can be perceived as a therapeutic opportunity, in contrast to the ischemic core defined as irreversibly damaged tissue, where the window for salvation is comparatively short. The pathologies in remote structures occur relatively frequently and are clearly linked to the post-stroke neurological outcome. In order to develop efficient therapies, a deeper understanding of what exactly happens in the exo-focal regions is necessary. The mechanisms of glia contribution to the ischemic damage in core/penumbra are relatively well described and include impaired ion homeostasis, excessive cell swelling, glutamate excitotoxic mechanism, release of pro-inflammatory cytokines and phagocytosis or damage propagation via astrocytic syncytia. However, little is known about glia involvement in post-ischemic processes in remote areas. In this literature review, we discuss the definitions of the terms "ischemic core", "penumbra" and "remote areas." Furthermore, we present evidence showing the array of structural and functional changes in the more remote regions from the primary site of focal ischemia, with a special focus on glia and the extracellular matrix. The collected information is compared with the processes commonly occurring in the ischemic core or in the penumbra. Moreover, the possible causes of this phenomenon and the approaches for investigation are described, and finally, we evaluate the efficacy of therapies, which have been studied for their anti-ischemic effect in remote areas in recent years.

Xeno-Free Biomimetic ECM Model for Investigation of Matrix Composition and Stiffness on Astrocyte Cell Response

Astrocytes, highly specialized glial cells, play a critical role in neuronal function. Variations in brain extracellular matrix (ECM) during development and disease can significantly alter astrocyte cell function. Age-related changes in ECM properties have been linked to neurodegenerative diseases such as Alzheimer's disease. The goal of this study was to develop hydrogel-based biomimetic ECM models with varying stiffness and evaluate the effects of ECM composition and stiffness on astrocyte cell response. Xeno-free ECM models were synthesized by combining varying ratios of human collagen and thiolated hyaluronic acid (HA) crosslinked with polyethylene glycol diacrylate. Results showed that modulating ECM composition yielded hydrogels with varying stiffnesses that match the stiffness of the native brain ECM. Collagen-rich hydrogels swell more and exhibit greater stability. Higher metabolic activity and greater cell spreading was observed in hydrogels with lower HA. Soft hydrogels trigger astrocyte activation indicated by greater cell spreading, high GFAP expression and low ALDH1L1 expression. This work presents a baseline ECM model to investigate the synergistic effects of ECM composition and stiffness on astrocytes, which could be further developed to identify key ECM biomarkers and formulate new therapies to alleviate the impact of ECM changes on the onset and progression of neurodegenerative diseases.

Growth Factor Binding Peptides in Poly (Ethylene Glycol) Diacrylate (PEGDA)-Based Hydrogels for an Improved Healing Response of Human Dermal Fibroblasts

Growth factors (GF) are critical cytokines in wound healing. However, the direct delivery of these biochemical cues into a wound site significantly increases the cost of wound dressings and can lead to a strong immunological response due to the introduction of a foreign source of GFs. To overcome this challenge, we designed a poly(ethylene glycol) diacrylate (PEGDA) hydrogel with the potential capacity to sequester autologous GFs directly from the wound site. We demonstrated that synthetic peptide sequences covalently tethered to PEGDA hydrogels physically retained human transforming growth factor beta 1 (hTGFβ1) and human vascular endothelial growth factor (hVEGF) at 3.2 and 0.6 ng/mm², respectively. In addition, we demonstrated that retained hTGFβ1 and hVEGF enhanced human dermal fibroblasts (HDFa) average cell surface area and proliferation, respectively, and that exposure to both GFs resulted in up to 1.9-fold higher fraction of area covered relative to the control. After five days in culture, relative to the control surface, non-covalently bound hTGFβ1 significantly increased the expression of collagen type I and hTGFβ1 and downregulated vimentin and matrix metalloproteinase 1 expression. Cumulatively, the response of HDFa to hTGFβ1 aligns well with the expected response of fibroblasts during the early stages of wound healing.

Brain Targeting of Citicoline Sodium via Hyaluronic Acid-Decorated Novel Nano-Transbilosomes for Mitigation of Alzheimer's Disease in a Rat Model: Formulation, Optimization, in vitro and in vivo Assessment

BACKGROUND

Alzheimer's disease (AD) is one of the furthermost advanced neurodegenerative disorders resulting in cognitive and behavioral impairment. Citicoline sodium (CIT) boosts the brain's secretion of acetylcholine, which aids in membrane regeneration and repair. However, it suffers from poor blood-brain barrier (BBB) permeation, which results in lower levels of CIT in the brain.

PURPOSE

This study targeted to encapsulate CIT into novel nano-platform transbilosomes decorated with hyaluronic acid CIT-HA*TBLs to achieve enhanced drug delivery from the nose to the brain.

METHODS

A method of thin-film hydration was utilized to prepare different formulae of CIT-TBLs using the Box-Behnken design. The optimized formula was then hyuloranated via integration of HA to form the CIT-HA*TBLs formula. Furthermore, AD induction was performed by aluminum chloride (Alcl3), animals were allocated, and brain hippocampus tissue was isolated for ELISA and qRT-PCR analysis of malondialdehyde (MDA), nuclear factor kappa B (NF-kB), and microRNA-137 (miR-137) coupled with immunohistochemical amyloid-beta (Aβ1-42) expression and histopathological finding.

RESULTS

The hyuloranated CIT-HA*TBLs formula, which contained the following ingredients: PL (300 mg), Sp 60 (43.97 mg), and SDC (20 mg). They produced spherical droplets at the nanoscale (178.94 ±12.4 nm), had a high entrapment efficiency with 74.92± 5.54%, had a sustained release profile of CIT with 81.27 ±3.8% release, and had ex vivo permeation of CIT with 512.43±19.58 μg/cm2. In vivo tests showed that CIT-HA*TBL thermogel dramatically reduces the hippocampus expression of miR-137 and (Aβ1-42) expression, boosting cholinergic neurotransmission and decreasing MDA and NF-kB production. Furthermore, CIT-HA*TBLs thermogel mitigate histopathological damage in compared to the other groups.

CONCLUSION

Succinctly, the innovative loading of CIT-HA*TBLs thermogel is a prospectively invaluable intranasal drug delivery system that can raise the efficacy of CIT in Alzheimer's management.