An overview of tissue and whole organ decellularization processes.

http://www.tara.tcd.ie/bitstream/handle/2262/54960/Biomaterials%20and%20scaffolds%20for%20tissue%20engineering.pdf;sequence=1

Biomaterials & scaffolds for tissue engineering

There is still an unresolved paradox with respect to the immunomodulating role of estrogens. On one side, we recognize inhibition of bone resorption and suppression of inflammation in several animal models of chronic inflammatory diseases. On the other hand, we realize the immunosupportive role of estrogens in trauma/sepsis and the proinflammatory effects in some chronic autoimmune diseases in humans. This review examines possible causes for this paradox. This review delineates how the effects of estrogens are dependent on criteria such as: 1) the immune stimulus (foreign antigens or autoantigens) and subsequent antigen-specific immune responses (e.g., T cell inhibited by estrogens vs. activation of B cell); 2) the cell types involved during different phases of the disease; 3) the target organ with its specific microenvironment; 4) timing of 17beta-estradiol administration in relation to the disease course (and the reproductive status of a woman); 5) the concentration of estrogens; 6) the variability in expression of estrogen receptor alpha and beta depending on the microenvironment and the cell type; and 7) intracellular metabolism of estrogens leading to important biologically active metabolites with quite different anti- and proinflammatory function. Also mentioned are systemic supersystems such as the hypothalamic-pituitary-adrenal axis, the sensory nervous system, and the sympathetic nervous system and how they are influenced by estrogens. This review reinforces the concept that estrogens have antiinflammatory but also proinflammatory roles depending on above-mentioned criteria. It also explains that a uniform concept as to the action of estrogens cannot be found for all inflammatory diseases due to the enormous variable responses of immune and repair systems.

/pdf/the-complex-role-of-estrogens-in-inflammation-29aw75ptuv.pdf

The complex role of estrogens in inflammation

Reprint of: Extracellular matrix as a biological scaffold material: Structure and function.

One theory of immune regulation involves homeostasis between T-helper 1 (Th1) and Thelper 2 (Th2) activity. The Th1/Th2 hypothesis arose from 1986 research suggesting mouse T-helper cells expressed differing cytokine patterns. This hypothesis was adapted to human immunity, with Th1- and Th2-helper cells directing different immune response pathways. Th1 cells drive the type-1 pathway (“cellular immunity”) to fight viruses and other intracellular pathogens, eliminate cancerous cells, and stimulate delayed-type hypersensitivity (DTH) skin reactions. Th2 cells drive the type-2 pathway (“humoral immunity”) and up-regulate antibody production to fight extracellular organisms; type 2 dominance is credited with tolerance of xenografts and of the fetus during pregnancy. Overactivation of either pattern can cause disease, and either pathway can down-regulate the other. But the hypothesis has major inconsistencies; human cytokine activities rarely fall into exclusive proTh1 or -Th2 patterns. The non-helper regulatory T cells, or the antigen-presenting cells (APC), likely influence immunity in a manner comparable to Th1 and Th2 cells. Many diseases previously classified as Th1 or Th2 dominant fail to meet the set criteria. Experimentally, Th1 polarization is readily transformed to Th2 dominance through depletion of intracellular glutathione, and vice versa. Mercury depletes glutathione and polarizes toward Th2 dominance. Several nutrients and hormones measurably influence Th1/Th2 balance, including plant sterols/ sterolins, melatonin, probiotics, progesterone, and the minerals selenium and zinc. The longchain omega-3 fatty acids EPA (eicosapentaenoic acid) and DHA (docosahexaenoic acid) significantly benefit diverse inflammatory and autoimmune conditions without any specific Th1/Th2 effect. Th1/Th2-based immunotherapies, e.g., T-cell receptor (TCR) peptides and interleukin-4 (IL4) injections, have produced mixed results to date. (Altern Med Rev 2003;8(3):223-246)

/pdf/th1-th2-balance-the-hypothesis-its-limitations-and-s134959i0l.pdf

Th1/Th2 balance: the hypothesis, its limitations, and implications for health and disease.

Macrophage phenotype and remodeling outcomes in response to biologic scaffolds with and without a cellular component

Macrophage phenotype can be characterized as proinflammatory (M1) or immunomodulatory and tissue remodeling (M2). The present study used a rat model to determine the macrophage phenotype at the site of implantation of two biologic scaffolds that were derived from porcine small intestinal submucosa (SIS) and that differed mainly according to their method of processing: the Restore device (SIS) and the CuffPatch device (carbodiimide crosslinked form of porcine-derived SIS (CDI-SIS)). An autologous tissue graft was used as a control implant. Immunohistologic methods were used to identify macrophage surface markers CD68 (pan macrophages), CD80 and CCR7 (M1 profile), and CD163 (M2 profile) during the remodeling process. All graft sites were characterized by the dense population of CD68+ mononuclear cells present during the first 4 weeks. The SIS device elicited a predominantly CD163+ response (M2 profile, p < 0.001) and showed constructive remodeling at 16 weeks. The CDI-SIS device showed a predominately CD80+ and CCR7+ response (M1 profile, p < 0.03), and at 16 weeks was characterized by chronic inflammation. The autologous tissue graft showed a predominately CD163+ response (M2) at 1 week, with a dual M1/M2 population (CD80+, CCR7+, and CD163+) by 2 and 4 weeks and moderately well organized connective tissue by 16 weeks. The processing methods used during the manufacturing of a biologic scaffold can have a profound influence upon the macrophage phenotype profile and downstream remodeling events. Routine histologic examination alone is inadequate to determine the phenotype of mononuclear cells that participate in the host response to the scaffold.

Macrophage Phenotype as a Determinant of Biologic Scaffold Remodeling

Biologic scaffolds composed of extracellular matrix (ECM) are widely used to facilitate remodeling and reconstruction of a variety of tissues in both preclinical animal studies and human clinical applications. The mechanisms by which such scaffolds influence the host tissue response are only partially understood, but it is logical that the mononuclear macrophage cell population plays a central role. The present study evaluated the role of macrophages that derive from peripheral blood in the degradation of ECM scaffolds. An established rat body wall reconstruction model was used to evaluate the degradation of carbodiimide (CDI)-crosslinked scaffolds composed of porcine small intestinal submucosa (SIS), noncrosslinked SIS, and autologous body wall. To assess the role of circulating macrophages in the degradation process, the degradation of each scaffold was assessed with and without macrophage depletion caused by administration of clodronate-containing liposomes. Results showed that peripheral blood monocytes are required for the early and rapid degradation of both SIS scaffolds and autologous body wall, and that CDI crosslinked SIS is resistant to macrophage-mediated degradation.

https://rethinkhealing.com/wp-content/uploads/2013/02/Valentin_TE-Part-A_2009.pdf

Macrophage Participation in the Degradation and Remodeling of Extracellular Matrix Scaffolds

Background: Extracellular matrix derived from porcine small intestinal submucosa is used for the repair of musculotendinous tissues. Preclinical evaluation and clinical use have suggested that small intestinal submucosa extracellular matrix degrades rapidly after implantation and can be replaced by host tissue that is functionally and histologically similar to the normal tissue.

Methods: The present study analyzed the temporal degradation of a ten-layer multilaminate device of small intestinal submucosa extracellular matrix used for the repair of canine Achilles tendon and examined the corresponding histological appearance of the remodeled tissue during the course of scaffold degradation. Devices were fabricated from small intestinal submucosa extracellular matrix labeled with 14C. The amount of 14C remaining in the remodeled graft was measured by liquid scintillation counting at three, seven, fourteen, twenty-eight, sixty, and ninety days after surgery. Blood, urine, feces, and other parenchymal tissues were also harvested to determine the fate of scaffold degradation products. Tissue specimens were prepared for routine histological analysis to examine the morphology of the remodeled graft at each time-point.

Results: The small intestinal submucosa extracellular matrix graft degraded rapidly, with approximately 60% of the mass lost by one month after surgery, and the graft was completely resorbed by three months after surgery. The graft supported rapid cellular infiltration and host tissue ingrowth. By ninety days after surgery, the remodeled small intestinal submucosa extracellular matrix consisted of a dense collagenous tissue with organization, cellularity, and vascularity similar to that of normal tendon.

Conclusions: Small intestinal submucosa extracellular matrix is rapidly degraded after implantation for the repair of a musculotendinous tissue in this canine Achilles tendon repair model and is replaced by the deposition and organization of host tissue that is histologically similar to that of normal tissue.

Clinical Relevance: The present study provides insight into the degradation and remodeling of extracellular matrix derived from porcine small intestinal submucosa, a biologic scaffold that has been used clinically for musculotendinous applications.

http://mckenzieillustrations.com/downloads/013 gilbert j bone joint surg 2007.pdf

Degradation and remodeling of small intestinal submucosa in canine Achilles tendon repair.

The carefully orchestrated events that regulate homeostasis of the immune system and the development of a protective immune response are coordinated to a large extent by cytokines produced by Thl, Th2, and the nominal Th3 lymphocyte subsets. An imbalance of Thl and Th2 may be responsible for both the occurrence as well as the progression of several diseases and their resultant complications. Patients with advanced cancer often have impaired cell-mediated immunity associated with a switch from Thl to Th2. On the other hand, shifting from one cytokine pattern to another may be highly beneficial in certain physiological conditions. For instance, IL-10, a Th2-type cytokine, may play a role in pregnancy-associated immune tolerance through the establishment of a Th2 cytokine bias at the maternal-fetal interface. Graft-versus-host disease (GVHD) is the major complication after allogeneic bone marrow transplantation (BMT) and is initiated by Thl cytokines and resultant dysregulation of the cytokine network. The balance between type 1 and type 2 cytokines governs the extent to which a cell-mediated immune response and a systemic inflammatory response develop after allogeneic BMT. Successful interventions to regulate Thl/Th2 balance and modify the immune response may thus decrease the risk of development or relapse of malignancy, avoid impairment of donor cell engraftment, and allow successful fetal maturation.

Ann M. Stewart-Akers

Papers

Macrophage phenotype and remodeling outcomes in response to biologic scaffolds with and without a cellular component

Macrophage Phenotype as a Determinant of Biologic Scaffold Remodeling

Macrophage Participation in the Degradation and Remodeling of Extracellular Matrix Scaffolds

Degradation and remodeling of small intestinal submucosa in canine Achilles tendon repair.

Th1/Th2 balance in cancer, transplantation and pregnancy.