Trapped in the Matrix: Neutrophil Extracellular Traps (NETs) and Fibrin in Wound Healing

The aim of this thesis was to investigate the effect of fibrin, NETs and the induction of NETosis, in wound healing. To achieve this, we created in vitro models to study the formation of NETs by several inducers, such as PMA, LPS, S. aureus, E. coli and N. meningitidis. Furthermore, we studied the role of NETs and extracellular DNA in sepsis and thrombosis. A diabetic rat model was used to study the effect of fibrin on wound healing

Functional differences between primary monocyte-derived and THP-1 macrophages and their response to LCPUFAs

Background: In immune cell models, macrophages are one of the most frequently used cell types. THP-1 cells are often used as model to study macrophage function, however they may act differently from primary human monocyte derived macrophages (MDMs). Methods: In this study, we investigated the intrinsic baseline differences between the human macrophage cell line THP-1 and human primary MDMs. Additionally, we studied the difference in response to treatment with long-chain polyunsaturated fatty acids (LCPUFAs): well-described immunomodulators. Results: Although the amount of cells that phagocytose were similar between the cell types, primary MDMs consumed significantly more E. coli bioparticles compared to THP-1 macrophages. In M1 macrophages, IL-12 secretion was almost fifty times higher by primary MDMs compared to THP-1 macrophages, thereby increasing the IL-12/IL-10 ratio. Despite this, the IL-12 secretion by THP-1 M1 macrophages was higher that the secretion of IL-10, thereby showing that it is still a suitable M1 type. Cytokine profiles differed between primary MDMs and THP-1 M1 and M2 macrophages. In response to LCPUFAs, primary M1 MDMs and THP-1 M1 macrophages were alike. Interestingly, primary M2 MDMs secreted less IL-10 and CCL22 when treated with LCPUFAs, whereas THP-1 M2 macrophages secreted more IL-10 when treated with LCPUFAs and showed no difference in CCL22 secretion. Conclusions: In conclusion, in an M1 setting, both THP-1 and primary MDMs are suitable models. However, when interested in M2 models, the model choice highly depends on the research question

Long Chain Polyunsaturated Fatty Acids (LCPUFAs) in the Prevention of Food Allergy

N-3 long chain polyunsaturated fatty acids (LCPUFAs) are considered to possess protective properties for human health by impacting on immunological reactions. An “inflammation-suppressive” effect appears to be the common denominator of the beneficial effects of most of these dietary components which may protect against the development of chronic immune disorders such as (food) allergy. LCPUFAs, especially n-3 LCPUFAs, have been shown to interact with both the sensitization as well as the effector phase in food allergy in pre-clinical models. In this review, we explore the anti-allergic properties of LCPUFAs by providing an overview of clinical, in vivo and in vitro studies. Furthermore, we discuss the susceptibility of LCPUFAs to lipid oxidation and possible strategies to support the efficacy of LCPUFAs in reducing the allergy risk by using additional components with anti-oxidative and anti-inflammatory capacities such as the flavonoid quercetin. Finally, we propose new strategies to prevent (food) allergy using combinations of LCPUFAs and additional nutrients in diets or supplements, and postulate to investigate the use of LCPUFAs in allergic symptom relief

In vitro induction of NETosis: Comprehensive live imaging comparison and systematic review

__Background__ Multiple inducers of in vitro Neutrophil Extracellular Trap (NET) formation (NETosis) have been described. Since there is much variation in study design and results, our aim was to create a systematic review of NETosis inducers and perform a standardized in vitro study of NETosis inducers important in (cardiac) wound healing. __Methods__ In vitro NETosis was studied by incubating neutrophils with PMA, living and dead bacteria (S. aureus and E. coli), LPS, (activated) platelets (supernatant), glucose and calcium ionophore Ionomycin using 3-hour periods of time-lapse confocal imaging. __Results__ PMA is a consistent and potent inducer of NETosis. Ionomycin also consistently resulted in extrusion of DNA, albeit with a process that differs from the NETosis process induced by PMA. In our standardized experiments, living bacteria were also potent inducers of NETosis, but dead bacteria, LPS, (activated) platelets (supernatant) and glucose did not induce NETosis. __Conclusion__ Our systematic review confirms that there is much variation in study design and results of NETosis induction. Our experimental results confirm that under standardized conditions, PMA, living bacteria and Ionomycin all strongly induce NETosis, but real-time confocal imaging reveal different courses of events

Dietary Advanced Glycation End products interacting with the intestinal epithelium: What do we really know?

Background: Advanced Glycation End products (AGEs) are a heterogeneous group of stable reaction products formed when amino acids, peptides, or proteins are glycated by the non-enzymatic Maillard Reaction. The formation and accumulation of these products in vivo are linked to many inflammation-based pathological outcomes and part of the pathophysiology of non-communicable diseases like eye cataracts and Alzheimer's disease. Since our diet contains high levels of the same compounds, it has been questioned whether their consumption is also detrimental to health. However, this is still under debate. In this context, the intestinal epithelium is an important target tissue since it is chronically exposed to relatively high concentrations of dietary AGEs. Scope of review: This review summarizes the current evidence on the impact of dietary AGEs on the intestinal epithelium and critically reflects on its methodology. Major conclusions: In healthy rodent models, an inflammation-independent impaired intestinal barrier function is claimed; however, dietary AGEs showed anti-inflammatory activity in IBD models. In vitro studies could be a valuable tool to unravel the underlying mechanisms of these effects, however the available studies face some limitations, e.g. lack of the physicochemical characterization of the glycated proteins, the inclusion of the proper controls and the dose-dependency of the effect. In addition, studies using more advanced in vitro models like intestinal organoids and co-cultures with immune cells exposed to gut microbial metabolites derived from the fermentation of AGEs are still needed

In Vitro Methodologies to Study the Role of Advanced Glycation End Products (AGEs) in Neurodegeneration

Advanced glycation end products (AGEs) can be present in food or be endogenously produced in biological systems. Their formation has been associated with chronic neurodegenerative diseases such as Alzheimer’s disease, Parkinson’s disease, multiple sclerosis, and amyotrophic lateral sclerosis. The implication of AGEs in neurodegeneration is related to their ability to bind to AGE-specific receptors and the ability of their precursors to induce the so-called “dicarbonyl stress”, resulting in cross-linking and protein damage. However, the mode of action underlying their role in neurodegeneration remains unclear. While some research has been carried out in observational clinical studies, further in vitro studies may help elucidate these underlying modes of action. This review presents and discusses in vitro methodologies used in research on the potential role of AGEs in neuroinflammation and neurodegeneration. The overview reveals the main concepts linking AGEs to neurodegeneration, the current findings, and the available and advisable in vitro models to study their role. Moreover, the major questions regarding the role of AGEs in neurodegenerative diseases and the challenges and discrepancies in the research field are discussed

Fibrin improves skin wound perfusion in a diabetic rat model

The fibrin matrix of the thrombus that is formed directly after wounding, is an important determinant of the success of the early phase of wound healing. This phase is often impaired in patients with diabetes. A promising approach to improve skin wound healing is the application of a pro-angiogenic fibrin matrix onto the wound. We studied this in 59 female WAG/RijCrl diabetic rats, in which we created two dorsal full-thickness wounds of which one was treated with a human physiological fibrin matrix (2 mg/ml) and one with PBS as control. Wound healing parameters were determined at different time points. The wound closure was significantly improved in fibrin-treated wounds on day 3 and 7. Also, fibrin-treated wounds showed a significantly higher perfusion on day 28 and 35 compared to control wounds (p < 0.05). CD68 staining revealed that human fibrin did not induce an immune response. In conclusion: the application of a fibrin matrix on a diabetic wound showed improved perfusion and an increased early closure rate of the wound area