Fenofibrate-loaded PLGA microparticles: effects on ischemic stroke

Biomaterials to Neuroprotect the Stroke Brain: A Large Opportunity for Narrow Time Windows

Ischemic stroke represents one of the most prevalent pathologies in humans and is a leading cause of death and disability. Anti-thrombolytic therapy with tissue plasminogen activator (t-PA) and surgical thrombectomy are the primary treatments to recanalize occluded vessels and normalize the blood flow in ischemic and peri-ischemic regions. A large majority of stroke patients are refractory to treatment or are not eligible due to the narrow time window of therapeutic efficacy. In recent decades, we have significantly increased our knowledge of the molecular and cellular mechanisms that inexorably lead to progressive damage in infarcted and peri-lesional brain areas. As a result, promising neuroprotective targets have been identified and exploited in several stroke models. However, these considerable advances have been unsuccessful in clinical contexts. This lack of clinical translatability and the emerging use of biomaterials in different biomedical disciplines have contributed to developing a new class of biomaterial-based systems for the better control of drug delivery in cerebral disorders. These systems are based on specific polymer formulations structured in nanoparticles and hydrogels that can be administered through different routes and, in general, bring the concentrations of drugs to therapeutic levels for prolonged times. In this review, we first provide the general context of the molecular and cellular mechanisms impaired by cerebral ischemia, highlighting the role of excitotoxicity, inflammation, oxidative stress, and depolarization waves as the main pathways and targets to promote neuroprotection avoiding neuronal dysfunction. In the second part, we discuss the versatile role played by distinct biomaterials and formats to support the sustained administration of particular compounds to neuroprotect the cerebral tissue at risk of damage.

The Potential of Biomaterial-Based Approaches as Therapies for Ischemic Stroke: A Systematic Review and Meta-Analysis of Pre-clinical Studies

Background: In recent years pre-clinical stroke research has shown increased interest in the development of biomaterial-based therapies to promote tissue repair and functional recovery. Such strategies utilize biomaterials as structural support for tissue regeneration or as delivery vehicles for therapeutic agents. While a range of biomaterials have been tested in stroke models, currently no overview is available for evaluating the benefit of these approaches. We therefore performed a systematic review and meta-analysis of studies investigating the use of biomaterials for the treatment of stroke in experimental animal models. Methods: Studies were identified by searching electronic databases (PubMed, Web of Science) and reference lists of relevant review articles. Studies reporting lesion volume and/or neurological score were included. Standardized mean difference (SMD) and 95% confidence intervals were calculated using DerSimonian and Laird random effects. Study quality and risk of bias was assessed using the CAMARADES checklist. Publication bias was visualized by funnel plots followed by trim and fill analysis of missing publications. Results: A total of 66 publications were included in the systematic review, of which 44 (86 comparisons) were assessed in the meta-analysis. Overall, biomaterial-based interventions improved both lesion volume (SMD: -2.98, 95% CI: -3.48, -2.48) and neurological score (SMD: -2.3, 95% CI: -2.85, -1.76). The median score on the CAMARADES checklist was 5.5/10 (IQR 4.25-6). Funnel plots of lesion volume and neurological score data revealed pronounced asymmetry and publication bias. Additionally, trim and fill analysis estimated 19 "missing" studies for the lesion volume outcome adjusting the effect size to -1.91 (95% CI: -2.44, -1.38). Conclusions: Biomaterials including scaffolds and particles exerted a positive effect on histological and neurological outcomes in pre-clinical stroke models. However, heterogeneity in the field, publication bias and study quality scores which may be another source of bias call for standardization of outcome measures and improved study reporting.

Fenofibrate-Loaded Biodegradable Nanoparticles for the Treatment of Experimental Diabetic Retinopathy and Neovascular Age-Related Macular Degeneration

Fenofibrate is a peroxisome proliferator-activated receptor α (PPARα) agonist and has been shown to have therapeutic effects on diabetic retinopathy (DR). However, the effects of fenofibrate through systemic administration are not as potent as desired due to inefficient drug delivery to the retina. The present study aimed to explore the sustained therapeutic effects of fenofibrate-loaded biodegradable nanoparticles (NP) on both DR and neovascular age-related macular degeneration (AMD). Fenofibrate was successfully encapsulated into poly(lactic- co-glycolic acid) (PLGA) NP (Feno-NP), and Feno-NP were optimized by varying polymer composition to achieve high drug loading and prolonged drug release. The Feno-NP made of PLGA 34 kDa demonstrated a drug content of 6% w/w and a sustained drug release up to 60 days in vitro. Feno-NP (PLGA 34 kDa) was selected for following in vivo studies, and one single intravitreal (IVT) injection of Feno-NP into rat eyes with a 30G fine needle maintained sustained fenofibric acid drug level in the eye for more than 60 days. The efficacy of Feno-NP in DR and neovascular AMD was investigated using streptozotocin (STZ)-induced diabetic rats, laser-induced choroidal neovascularization (CNV) rats, and very low-density lipoprotein receptor knockout ( Vldlr ^-/-) mice. Therapeutic effects of Feno-NP were evaluated by measuring electroretinogram (ERG), retinal vascular leakage, leukostasis, CNV size, and retinal levels of vascular endothelial growth factor (VEGF) and intracellular adhesion molecule-1 (ICAM-1). In diabetic rats, Feno-NP ameliorated retinal dysfunctions, reduced retinal vascular leakage, inhibited retinal leukostasis, and downregulated the overexpression of VEGF and ICAM-1 at 8 weeks after one IVT injection. In addition, Feno-NP reduced retinal vascular leakage and CNV formation in both CNV rats and Vldlr ^-/- mice. Moreover, no toxicity of Feno-NP or Blank-NP to retinal structure and function was detected. Feno-NP exhibited good physiochemical characteristics and controlled drug release profile, conferring prolonged beneficial effects on DR and neovascular AMD.

Biomaterial Applications in Cell-Based Therapy in Experimental Stroke

Stroke is an important health issue corresponding to the second cause of mortality and first cause of severe disability with no effective treatments after the first hours of onset. Regenerative approaches such as cell therapy provide an increase in endogenous brain structural plasticity but they are not enough to promote a complete recovery. Tissue engineering has recently aroused a major interesting development of biomaterials for use into the central nervous system. Many biomaterials have been engineered based on natural compounds, synthetic compounds, or a mix of both with the aim of providing polymers with specific properties. The mechanical properties of biomaterials can be exquisitely regulated forming polymers with different stiffness, modifiable physical state that polymerizes in situ, or small particles encapsulating cells or growth factors. The choice of biomaterial compounds should be adapted for the different applications, structure target, and delay of administration. Biocompatibilities with embedded cells and with the host tissue and biodegradation rate must be considerate. In this paper, we review the different applications of biomaterials combined with cell therapy in ischemic stroke and we explore specific features such as choice of biomaterial compounds and physical and mechanical properties concerning the recent studies in experimental stroke.

Concentration-dependent rheological properties of ECM hydrogel for intracerebral delivery to a stroke cavity

Biomaterials composed of mammalian extracellular matrix (ECM) promote constructive tissue remodeling with minimal scar tissue formation in many anatomical sites. However, the optimal shape and form of ECM scaffold for each clinical application can vary markedly. ECM hydrogels have been shown to promote chemotaxis and differentiation of neuronal stem cells, but minimally invasive delivery of such scaffold materials to the central nervous system (CNS) would require an injectable form. These ECM materials can be manufactured to exist in fluid phase at room temperature, while forming hydrogels at body temperature in a concentration-dependent fashion. Implantation into the lesion cavity after a stroke could hence provide a means to support endogenous repair mechanisms. Herein, we characterize the rheological properties of an ECM hydrogel composed of urinary bladder matrix (UBM) that influence its delivery and in vivo interaction with host tissue. There was a notable concentration-dependence in viscosity, stiffness, and elasticity; all characteristics important for minimally invasive intracerebral delivery. An efficient MRI-guided injection with drainage of fluid from the cavity is described to assess in situ hydrogel formation and ECM retention at different concentrations (0, 1, 2, 3, 4, and 8mg/mL). Only ECM concentrations >3mg/mL gelled within the stroke cavity. Lower concentrations were not retained within the cavity, but extensive permeation of the liquid phase ECM into the peri-infarct area was evident. The concentration of ECM hydrogel is hence an important factor affecting gelation, host-biomaterial interface, as well intra-lesion distribution.

STATEMENT OF SIGNIFICANCE

Extracellular matrix (ECM) hydrogel promotes constructive tissue remodeling in many tissues. Minimally invasive delivery of such scaffold materials to the central nervous system (CNS) would require an injectable form that exists in fluid phase at room temperature, while forming hydrogels at body temperature in a concentration-dependent fashion. We here report the rheological characterization of an injectable ECM hydrogel and its concentration-dependent delivery into a lesion cavity formed after a stroke based on MRI-guidance. The concentration of ECM determined its retention within the cavity or permeation into tissue and hence influenced its interaction with the host brain. This study demonstrates the importance of understanding the structure-function relationship of biomaterials to guide particular clinical applications.

The role of PPAR activation during the systemic response to brain injury

Background

Fenofibrate, a PPAR-α activator, has shown promising results as a neuroprotective therapy, with proposed anti-inflammatory and anti-oxidant effects. However, it displays poor blood-brain barrier permeability leading to some ambiguity over its mechanism of action. Experimentally induced brain injury has been shown to elicit a hepatic acute phase response that modulates leukocyte recruitment to the injured brain. Here, we sought to discover whether one effect of fenofibrate might include the suppression of the acute phase response (APR) following brain injury.

Methods

A 1-h intraluminal thread middle cerebral artery occlusion (MCAO) model followed by a 6-h reperfusion was performed in C57/BL6 mice. Quantitative reverse transcriptase-polymerase chain reaction was then used to measure hepatic expression of chemokine (C-X-C motif) ligand 1 (CXCL1), chemokine ligand 10 (CXCL10) and serum amyloid A-1 (SAA-1), and immunohistochemical analysis was used to quantify brain and hepatic neutrophil infiltration following stroke.

Results

The MCAO and sham surgery induced the expression of all three acute phase reactants. A 14-day fenofibrate pre-treatment decreased reactant production, infarct volume, and neutrophil recruitment to the brain and liver, which is a hallmark of the APR.

Conclusions

The data highlight a novel mechanism of action for fenofibrate and lend further evidence towards the promotion of its use as a prophylactic therapy in patients at risk of cerebral ischaemia. Further research is required to elucidate the mechanistic explanation underlying its actions.

Effects of the PPAR-α agonist fenofibrate on acute and short-term consequences of brain ischemia

In stroke, there is an imperative need to develop disease-modifying drugs able to (1) induce neuroprotection and vasculoprotection, (2) modulate recovery and brain plasticity, and (3) limit the short-term motor and cognitive consequences. We hypothesized that fenofibrate, a peroxisome proliferator-activated receptor-α (PPAR-α) agonist, could exert a beneficial effect on immediate and short-term poststroke consequences related to its pleiotropic mechanisms. Rats or mice were subjected to focal ischemia to determine the effects of acute treatment by fenofibrate on (i) motor and memory impairment, (2) both cerebral and vascular compartments, (3) inflammation, (4) neurogenesis, and (5) amyloid cascade. We show that fenofibrate administration results in both neuronal and vascular protection and prevents the short-term motor and cognitive poststroke consequences by interaction with several mechanisms. Modulation of PPAR-α generates beneficial effects in the immediate poststroke consequences by mechanisms involving the interactions between polynuclear neutrophils and the vessel wall, and microglial activation. Fenofibrate modulates mechanisms involved in neurorepair and amyloid cascade. Our results suggest that PPAR-α agonists could check the key points of a potential disease-modifying effect in stroke.

Drug delivery systems for the treatment of ischemic stroke

Stroke is the third leading cause of death in the United States. Reduced cerebral blood flow causes acute damage to the brain due to excitotoxicity, reactive oxygen species (ROS), and ischemia. Currently, the main treatment for stroke is to revive the blood flow by using thrombolytic agents. Reviving blood flow also causes ischemia-reperfusion (I/R) damage. I/R damage results from inflammation and apoptosis and can persist for days to weeks, increasing the infarct size. Drugs can be applied to stroke to intervene in the sub-acute and chronic phases. Chemical, peptide, and genetic therapies have been evaluated to reduce delayed damage to the brain. These drugs have different characteristics, requiring that delivery carriers be developed based on these characteristics. The delivery route is another important factor affecting the efficiency of drug delivery. Various delivery routes have been developed, such as intravenous injection, intranasal administration, and local direct injection to overcome the blood-brain-barrier (BBB). In this review, the delivery carriers and delivery routes for peptide and gene therapies are discussed and examples are provided. Combined with new drugs, drug delivery systems will eventually provide useful treatments for ischemic stroke.

Current advances in research and clinical applications of PLGA-based nanotechnology

Co-polymer poly(lactic-co-glycolic acid) (PLGA) nanotechnology has been developed for many years and has been approved by the US FDA for the use of drug delivery, diagnostics and other applications of clinical and basic science research, including cardiovascular disease, cancer, vaccine and tissue engineering. This article presents the more recent successes of applying PLGA-based nanotechnologies and tools in these medicine-related applications. It focuses on the possible mechanisms, diagnosis and treatment effects of PLGA preparations and devices. This updated information will benefit to both new and established research scientists and clinical physicians who are interested in the development and application of PLGA nanotechnology as new therapeutic and diagnostic strategies for many diseases.