Zymosan-induced inflammation stimulates neo-adipogenesis

Modic changes: From potential molecular mechanisms to future research directions (Review)

Low back pain (LBP) is a leading cause of disability worldwide. Although not all patients with Modic changes (MCs) experience LBP, MC is often closely associated with LBP and disc degeneration. In clinical practice, the focus is usually on symptoms related to MC, which are hypothesized to be associated with LBP; however, the link between MC and nerve compression remains unclear. In cases of intervertebral disc herniation, nerve compression is often the definitive cause of symptoms. Recent advances have shed light on the pathophysiology of MC, partially elucidating its underlying mechanisms. The pathogenesis of MC involves complex bone marrow‑disc interactions, resulting in bone marrow inflammation and edema. Over time, hematopoietic cells are gradually replaced by adipocytes, ultimately resulting in localized bone marrow sclerosis. This process creates a barrier between the intervertebral disc and the bone marrow, thereby enhancing the stability of the vertebral body. The latest understanding of the pathophysiology of MC suggests that chronic inflammation plays a significant role in its development and hypothesizes that the complement system may contribute to its pathological progression. However, this hypothesis requires further research to be confirmed. The present review we proposed a pathological model based on current research, encompassing the transition from Modic type 1 changes (MC1) to Modic type 2 changes (MC2). It discussed key cellular functions and their alterations in the pathogenesis of MC and outlined potential future research directions to further elucidate its mechanisms. Additionally, it reviewed the current clinical staging and pathogenesis of MC, recommended the development of an updated staging system and explored the prospects of integrating emerging artificial intelligence technologies.

Decellularized Extracellular Matrix Scaffolds for Soft Tissue Augmentation: From Host-Scaffold Interactions to Bottlenecks in Clinical Translation

Along with a paradigm shift in looking at soft tissue fillers from space-filling to bioactive materials, decellularized extracellular matrix (DEM) fillers have gained more attention considering their superior bioactivity. However, the complex mechanisms that govern the interaction between host tissues and DEMs have been partially understood. This review first covers the mechanisms that determine immunogenicity, angiogenesis and vasculogenesis, and recellularization and remodeling after DEM implantation into host tissue, with a particular focus on related findings from filler materials. Accordingly, the review delves into the dual role of macrophages and their M1/M2 polarization paradigm to form both constructive and destructive immune responses to DEM implants. Moreover, the contribution of macrophages in angiogenesis has been elucidated, which includes but is not limited to the secretion of angiogenic growth factors and extracellular matrix (ECM) remodeling. The findings challenge the traditional view of immune cells as solely destructive entities in biomaterials and indicate their multifaceted roles in tissue regeneration. Furthermore, the review discusses how the compositional factors of DEMs, such as the presence of growth factors and matrikines, can influence angiogenesis, cell fate, and differentiation during the recellularization process. It is also shown that the biomechanical properties of DEMs, including tissue stiffness, modulate cell responses through mechanotransduction pathways, and the structural properties of DEMs, such as scaffold porosity, impact cell-cell and cell-ECM interactions. Finally, we pointed out the current clinical applications, the bottlenecks in the clinical translation of DEM biomaterials into soft tissue fillers, as well as the naïve research areas of the field.

Construction of a vascularized fascia-prosthesis compound model with axial pedicle for ear reconstruction surgery

Background: To design a vascular pedicled fascia-prosthesis compound model that can be used for ear reconstruction surgery. Methods: A vascularized tissue engineering chamber model was constructed in New Zealand rabbits, and fresh tissues were obtained after 4 weeks. The histomorphology and vascularization of the newly born tissue compound were analyzed and evaluated by tissue staining and Micro-CT scanning. Results: The neoplastic fibrous tissue formed in the vascularized tissue engineering chamber with the introduction of abdominal superficial vessels, similar to normal fascia, was superior to the control group in terms of vascularization, vascular density, total vascular volume, and total vascular volume/total tissue volume. Conclusion: In vivo, introducing abdominal superficial vessels in the tissue engineering chamber prepped for ear prosthesis may form a well-vascularized pedicled fascia-prosthesis compound that can be used for ear reconstruction.

Basivertebral Nerve Ablation

Low back pain is one of the most prevalent musculoskeletal ailments in the United States. Intraosseous radiofrequency ablation of the basivertebral nerve is an effective and durable therapy for low back pain and can be offered to patients who have chronic low back pain of greater than 6 months of duration, failure to respond to noninvasive therapies for 6 months, with either Modic Type I or Type II changes at L3-S1. This article reviews the anatomy and physiology, patient selection, technique, and evidence regarding basivertebral nerve ablation.

[Research progress of external volume expansion assisted autologous fat grafting for breast reconstruction]

OBJECTIVE

To review the application progress, mechanism, application points, limitations, and oncological safety of external volume expansion (EVE) assisted autologous fat grafting for breast reconstruction and provide a reference for optimizing the design of EVE.

METHODS

Based on the latest relevant articles, the basic experiments and clinical applications of EVE were summarized.

RESULTS

EVE can reduce interstitial fluid pressure, increase blood supply, and promote adipogenic differentiation, thereby benefiting the survival of transplanted fat. EVE assisted autologous fat grafting in clinical practice can improve the retention rate of breast volume and the outcome of breast reconstruction, meanwhile it doesn't increase the risk of local recurrence. But there is no standard parameters for application, and there are many complications and limitations.

CONCLUSION

EVE improves the survival of transplanted fat, but its complications and poor compliance are obvious, so it is urgent to further investigate customized products for breast reconstruction after breast cancer and establish relevant application guidelines.

Basivertebral Nerve Ablation for the Treatment of Vertebrogenic Pain

Chronic low back pain affects a significant portion of patients worldwide and is a major contributor to patient disability; however, it is a difficult problem to diagnose and treat. The prevailing model of chronic low back pain has presumed to follow a discogenic model, but recent studies have shown a vertebrogenic model that involves the basivertebral nerve (BVN). Radiofrequency ablation of the BVN has emerged as a possible nonsurgical therapy for vertebrogenic low back pain. The objective of this manuscript is to provide a comprehensive review of vertebrogenic pain diagnosis and our current understanding of BVN ablation as treatment.

Adipose Stromal Cells Enhance Decellularized Adipose Tissue Remodeling Through Multimodal Mechanisms

Decellularized adipose tissue (DAT) scaffolds represent a promising cell-instructive platform for soft tissue engineering. While recent work has highlighted that mesenchymal stromal cells, including adipose-derived stromal cells (ASCs), can be combined with decellularized scaffolds to augment tissue regeneration, the mechanisms involved require further study. The objective of this work was to probe the roles of syngeneic donor ASCs and host-derived macrophages in tissue remodeling of DAT scaffolds within an immunocompetent mouse model. Dual transgenic reporter mouse strains were employed to track and characterize the donor ASCs and host macrophages within the DAT implants. More specifically, ASCs isolated from dsRed mice were seeded on DAT scaffolds, and the seeded and unseeded control scaffolds were implanted subcutaneously into MacGreen transgenic mice for up to 8 weeks. ASC seeding was shown to augment cell infiltration into the DAT implants at 8 weeks, and this was linked to significantly enhanced angiogenesis relative to the unseeded controls. Immunohistochemical staining demonstrated long-term retention of the syngeneic donor ASCs over the duration of the 8-week study, providing evidence that the DAT scaffolds are a cell-supportive delivery platform. Notably, newly formed adipocytes within the DAT implants were not dsRed⁺, indicating that the donor ASCs supported fat formation through indirect mechanisms. Immunohistochemical tracking of host macrophages through costaining for enhanced green fluorescent protein with the macrophage marker Iba1 revealed that ASC seeding significantly increased the number of infiltrating macrophages within the DAT implants at 3 weeks, while the fraction of macrophages relative to the total cellular infiltrate was similar between the groups at 1, 3, and 8 weeks. Consistent with the tissue remodeling response that was observed, western blotting demonstrated that there was significantly augmented expression of CD163 and CD206, markers of constructive M2-like macrophages, within the ASC-seeded DAT implants. Overall, our results demonstrate that exogenous ASCs enhance tissue regeneration within DAT scaffolds indirectly through multimodal mechanisms that include host cell recruitment and immunomodulation. These data provide further evidence to support the use of decellularized scaffolds as a delivery platform for ASCs in tissue engineering.

In vivo tissue engineering of an adipose tissue flap using fat grafts and Adipogel

For decades, plastic surgeons have spent considerable effort exploring anatomical regions for free flap design. More recently, tissue-engineering approaches have been utilised in an attempt to grow transplantable tissue flaps in vivo. The aim of this study was to engineer a fat flap with a vascular pedicle by combining autologous fat grafts and a novel acellular hydrogel (Adipogel) in an established tissue-engineering model comprising a chamber and blood vessel loop. An arteriovenous loop was created in the rat groin from the femoral vessels and positioned inside a perforated polycarbonate chamber. In Group 1, the chamber contained minced, centrifuged autologous fat; in Group 2, Adipogel was added to the graft; and in Group 3, Adipogel alone was used. Constructs were histologically examined at 6 and 12 weeks. In all groups, new tissue was generated. Adipocytes, although appearing viable in the graft at the time of insertion, were predominantly nonviable at 6 weeks. However, by 12 weeks, new fat had formed in all groups and was significantly greater in the combined fat/Adipogel group. No significant difference was seen in final construct total volume or construct neovascularisation between the groups. This study demonstrated that a pedicled adipose flap can be generated in rats by combining a blood vessel loop, an adipogenic hydrogel, and a lipoaspirate equivalent. Success appears to be based on adipogenesis rather than on adipocyte survival, and consistent with our previous work, this adipogenesis occurred subsequent to graft death and remodelling. The regenerative process was significantly enhanced in the presence of Adipogel.

Increase of glandular epithelial cell clusters by an external volume expansion device promotes adipose tissue regeneration by recruiting macrophages

Background: There is a clinical need for the use of engineered adipose tissue in place of surgical reconstruction. We previously found that the external volume expansion (EVE) device increased special cell clusters in well-vascularized connective stroma during adipose regeneration. However, the origin of these cell clusters and their role in adipose tissue regeneration remain unknown. Aim: In the present study, we evaluated EVE in the construction of expanded prefabricated adipose tissue (EPAT) in a rat model. Methods: Rats were randomized into an EVE suction group and a control group, with 24 rats in each group. The structure and origin of the special cell clusters were determined by hematoxylin and eosin staining, and immunohistochemistry; their role in adipose tissue regeneration was investigated by immunohistochemistry and Western blot analyses. Results: Special cell clusters began to increase at week 1 with a peak at week 4, and then receded from weeks 8 to 12. Clusters were identified as glandular epithelial cells as determined by their gland-like structure and expression of specific markers. The cell clusters induced significant infiltration of macrophage antigen-2 (Mac-2) positive macrophages by secreting monocyte chemoattractant protein-1 (MCP-1) at the early stage of suction. Subsequently, these infiltrated macrophages expressed massive vascular endothelial growth factor (VEGF) to promoted angiogenesis. Conclusion: EVE generated glandular epithelial cell clusters, which recruited macrophages to promote angiogenesis and subsequent adipose tissue regeneration. These findings shed light on the mechanisms underlying the effects of EVE devices on adipose tissue regeneration.

Alpha lipoic acid and metformin alleviates experimentally induced insulin resistance and cognitive deficit by modulation of TLR2 signalling

BACKGROUND

Obesity is commonly found to be co-morbid with type 2 Diabetes Mellitus. In obese diabetic patients, TLR-2 receptor induced inflammation leads to the development of insulin resistance (IR). Furthermore, the IR is considered to be the most important cause for promoting cognitive decline which is evident in brain of patients with Alzheimer's disease related dementia (ADRD).

METHODS

In this study, the effect of α-lipoic acid (ALA) has been examined in rodent model of zymosan induced insulin resistance and cognitive deficits, targeting at TLR-2 signalling. TLR-2 agonist, Zymosan initiates inflammatory cascade, resulting in IR and cognitive dysfunction. Zymosan (50 mg/kg ip) was given to mice on 1st, 8th, 15th and 22nd day to induce IR which was confirmed by hyperglycaemia, hyperinsulinemia, hyperlipidimea, increased glycated haemoglobin and HOMA-IR. Further the cognitive performance was assessed in Morris water maze revealing cognitive deficit in zymosan treated mice.

RESULTS

Daily treatment with ALA for 28 days (50, 100, 200 mg/kg, ip) significantly improved insulin sensitivity and cognitive performance in mice by decreasing insulin resistance, corticosterone, IL-6 levels, acetylcholinesterase enzyme activity and oxidative stress in liver, cortex and hippocampus. ALA also increased adiponectin level and reduced body weight. Combination of ALA (100 mg/kg, ip) with metformin (100 mg/kg, ip) exhibited a potentiating effect in improving cognitive performance and insulin signalling.

CONCLUSION

The findings of the study supported the hypothesis that TLR-2 induced inflammation leads to insulin resistance and cognitive impairment and provides an evidence for the therapeutic effect of ALA in IR and ADRD patients.

Biocompatibility of injectable hydrogel from decellularized human adipose tissue in vitro and in vivo

Adipose tissue engineering is considered as a promising treatment for repairing soft tissue defects. The decellularized extracellular matrix (ECM) is becoming the research focus in tissue engineering for its tissue specificity. In this study, the human adipose tissue liposucted from healthy people were decellularized by a series of mechanical, chemical, and enzymatic methods. The components of cell and lipid were effectively removed, whereas the collagens and other ingredients in adipose tissue were retained in the human decellularized adipose tissue (hDAT). Then the extracted hDAT was further fabricated into injectable hydrogel, which could be self-assembled to form gel under certain condition. The hDAT hydrogel was nontoxic to human adipose-derived stem cells (ADSCs) and could spontaneously induce adipogenic differentiation in vitro. It was highly biocompatible and could not cause inflammation and rejection after being implanted subcutaneously. The hDAT hydrogel developed in this study will be one of the available choices for soft tissue enlargement and cosmetic fillers because of its noninvasive in collection and implantation process. © 2018 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater 107B: 1684-1694, 2019.

Polycaprolactone nanofibrous mesh reduces foreign body reaction and induces adipose flap expansion in tissue engineering chamber

Tissue engineering chamber technique can be used to generate engineered adipose tissue, showing the potential for the reconstruction of soft tissue defects. However, the consequent foreign body reaction induced by the exogenous chamber implantation causes thick capsule formation on the surface of the adipose flap following capsule contracture, which may limit the internal tissue expansion. The nanotopographical property and architecture of nanofibrous scaffold may serve as a promising method for minimizing the foreign body reaction. Accordingly, electrospinning porous polycaprolactone (PCL) nanofibrous mesh, a biocompatible synthetic polymer, was attached to the internal surface of the chamber for the reducing local foreign body reaction. Adipose flap volume, level of inflammation, collagen quantification, capsule thickness, and adipose tissue-specific gene expression in chamber after implantation were evaluated at different time points. The in vivo study revealed that the engineered adipose flaps in the PCL group had a structure similar to that in the controls and normal adipose tissue structure but with a larger flap volume. Interleukin (IL)-1β, IL-6, and transforming growth factor-β expression decreased significantly in the PCL group compared with the control. Moreover, the control group had much more collagen deposition and thicker capsule than that observed in the PCL group. These results indicate that the unique nanotopographical effect of electrospinning PCL nanofiber can reduce foreign body reaction in a tissue engineering chamber, which maybe a promising new method for generating a larger volume of mature, vascularized, and stable adipose tissue.

Pathobiology of Modic changes

PURPOSE

Low back pain (LBP) is the most disabling condition worldwide. Although LBP relates to different spinal pathologies, vertebral bone marrow lesions visualized as Modic changes on MRI have a high specificity for discogenic LBP. This review summarizes the pathobiology of Modic changes and suggests a disease model.

METHODS

Non-systematic literature review.

RESULTS

Chemical and mechanical stimulation of nociceptors adjacent to damaged endplates are likely a source of pain. Modic changes are adjacent to a degenerated intervertebral disc and have three generally interconvertible types suggesting that the different Modic change types represent different stages of the same pathological process, which is characterized by inflammation, high bone turnover, and fibrosis. A disease model is suggested where disc/endplate damage and the persistence of an inflammatory stimulus (i.e., occult discitis or autoimmune response against disc material) create predisposing conditions. The risk to develop Modic changes likely depends on the inflammatory potential of the disc and the capacity of the bone marrow to respond to it. Bone marrow lesions in osteoarthritic knee joints share many characteristics with Modic changes adjacent to degenerated discs and suggest that damage-associated molecular patterns and marrow fat metabolism are important pathogenetic factors. There is no consensus on the ideal therapy. Non-surgical treatment approaches including intradiscal steroid injections, anti-TNF-α antibody, antibiotics, and bisphosphonates have some demonstrated efficacy in mostly non-replicated clinical studies in reducing Modic changes in the short term, but with unknown long-term benefits. New diagnostic tools and animal models are required to improve painful Modic change identification and classification, and to clarify the pathogenesis.

CONCLUSION

Modic changes are likely to be more than just a coincidental imaging finding in LBP patients and rather represent an underlying pathology that should be a target for therapy.

Human glandular organoid formation in murine engineering chambers after collagenase digestion and flow cytometry isolation of normal human breast tissue single cells

Women with high mammographic density (MD) are at increased risk of breast cancer (BC) after adjustment for age and body mass index. We have developed a murine biochamber model in which both high MD (HMD) and low MD (LMD) tissue can be propagated. Here, we tested whether cells isolated by collagenase digestion and fluorescence-activated cell sorting (FACS) from normal breast can be reconstituted in our biochamber model, which would allow cell-specific manipulations to be tested. Fresh breast tissue was collected from women (n = 7) undergoing prophylactic mastectomy. The tissue underwent collagenase digestion overnight and, in some cases, additional FACS enrichment to obtain mature epithelial, luminal progenitor, mammary stem, and stromal cells. Cells were then transferred bilaterally into biochambers in SCID mice (n = 5-7) and incubated for 6 weeks, before harvesting for histological analyses, and immunohistochemical staining for cytokeratins (CK), vimentin, Ki-67, murine macrophages, and Cleaved Caspase-3. Biochambers inoculated with single cells after collagenase digestion or with flow cytometry contained glandular structures of human origin (human vimentin-positive), which expressed CK-14 and pan-CK, and were proliferating (Ki-67-positive). Glandular structures from the digested tissues were smaller than those in chambers seeded with finely chopped intact mammary tissue. Mouse macrophage infiltration was higher in the chambers arising from digested tissues. Pooled single cells and FACS fractionated cells were viable in the murine biochambers and formed proliferating glandular organoids of human origin. This is among the first report to demonstrate the success of formed human glandular organoids from isolated primary mammary cells in the murine biochamber model.

Possible role of mechanical force in regulating regeneration of the vascularized fat flap inside a tissue engineering chamber

In plastic and reconstructive surgery, adipose tissue is widely used as effective filler for tissue defects. Strategies for treating soft tissue deficiency, which include free adipose tissue grafts, use of hyaluronic acid, collagen injections, and implantation of synthetic materials, have several clinical limitations. With the aim of overcoming these limitations, researchers have recently utilized tissue engineering chambers to produce large volumes of engineered vascularized fat tissue. However, the process of growing fat tissue in a chamber is still relatively limited, and can result in unpredictable or dissatisfactory final tissue volumes. Therefore, detailed understanding of the process is both necessary and urgent. Many studies have shown that mechanical force can change the function of cells via mechanotransduction. Here, we hypothesized that, besides the inflammatory response, one of the key factors to control the regeneration of vascularized fat flap inside a tissue engineering chamber might be the balance of mechanical forces. To test our hypothesis, we intend to change the balance of forces by means of measures in order to make the equilibrium point in favor of the direction of regeneration. If those measures proved to be feasible, they could be applied in clinical practice to engineer vascularized adipose tissue of predictable size and shape, which would in turn help in the advancement of tissue engineering.

Diffusion and perfusion: the keys to fat grafting

BACKGROUND

Fat grafting is now widely used in plastic surgery. Long-term graft retention can be unpredictable. Fat grafts must obtain oxygen via diffusion until neovascularization occurs, so oxygen delivery may be the overarching variable in graft retention.

METHODS

We studied the peer-reviewed literature to determine which aspects of a fat graft and the microenvironment surrounding a fat graft affect oxygen delivery and created 3 models relating distinct variables to oxygen delivery and graft retention.

RESULTS

Our models confirm that thin microribbons of fat maximize oxygen transport when injected into a large, compliant, well-vascularized recipient site. The "Microribbon Model" predicts that, in a typical human, fat injections larger than 0.16 cm in radius will have a region of central necrosis. Our "Fluid Accommodation Model" predicts that once grafted tissues approach a critical interstitial fluid pressure of 9 mm Hg, any additional fluid will drastically increase interstitial fluid pressure and reduce capillary perfusion and oxygen delivery. Our "External Volume Expansion Effect Model" predicts the effect of vascular changes induced by preoperative external volume expansion that allow for greater volumes of fat to be successfully grafted.

CONCLUSIONS

These models confirm that initial fat grafting survival is limited by oxygen diffusion. Preoperative expansion increases oxygen diffusion capacity allowing for additional graft retention. These models provide a scientific framework for testing the current fat grafting theories.

The adipogenic potential of various extracellular matrices under the influence of an angiogenic growth factor combination in a mouse tissue engineering chamber

The extracellular matrix (ECM) Matrigel™ has frequently and successfully been used to generate new adipose tissue experimentally, but is unsuitable for human application. This study sought to compare the adipogenic potential of a number of alternative, biologically derived or synthetic ECMs with potential for human application, with and without growth factors and a small fat autograft. Eight groups, with six severe combined immunodeficient (SCID) mice per group, were created with bilateral chambers (silicone tubes) implanted around the epigastric vascular pedicle, with one chamber/animal containing a 5mg fat autograft. Two animal groups were created for each of four ECMs (Matrigel™, Myogel, Cymetra® and PuraMatrix™) which filled the bilateral chambers. One group/ECM had no growth factors added to chambers whilst the other group had growth factors (GFs) (vascular endothelial growth factor-A (VEGF-A) plus fibroblast growth factor-2 (FGF-2) plus platelet-derived growth factor-BB (PDGF-BB)) added to both chambers. At 6weeks, chamber tissue was morphometrically assessed for percent and absolute adipose tissue volume. Overall, the triple GF regime significantly increased percent(∗) and absolute(#) adipose tissue volume (p<0.0005(∗#)) compared to chambers without triple GF treatment. The fat autograft also significantly increased percent (p<0.0005) and absolute (p<0.011) adipose tissue volume. Cymetra® (human collagen) constructs yielded the largest total tissue and absolute adipose tissue volume. We found that the pro-angiogenic FGF-2, VEGF-A and PDGF-BB combination in ECMs of synthetic and biological origin produced an overall significantly increased adipose tissue volume at 6weeks and may have clinical application, particularly with Cymetra.

Tissue engineering chamber promotes adipose tissue regeneration in adipose tissue engineering models through induced aseptic inflammation

Tissue engineering chamber (TEC) makes it possible to generate significant amounts of mature, vascularized, stable, and transferable adipose tissue. However, little is known about the role of the chamber in tissue engineering. Therefore, to investigate the role of inflammatory response and the change in mechanotransduction started by TEC after implantation, we placed a unique TEC model on the surface of the groin fat pads in rats to study the expression of cytokines and tissue development in the TEC. The number of infiltrating cells was counted, and vascular endothelial growth factor (VEGF) and monocyte chemotactic protein-1 (MCP-1) expression levels in the chamber at multiple time points postimplantation were analyzed by enzyme-linked immunosorbent assay. Tissue samples were collected at various time points and labeled for specific cell populations. The result showed that new adipose tissue formed in the chamber at day 60. Also, the expression of MCP-1 and VEGF in the chamber decreased slightly from an early stage as well as the number of the infiltrating cells. A large number of CD34+/perilipin- perivascular cells could be detected at day 30. Also, the CD34+/perilipin+ adipose precursor cell numbers increased sharply by day 45 and then decreased by day 60. CD34-/perilipin+ mature adipocytes were hard to detect in the chamber content at day 30, but their number increased and then peaked at day 60. Ki67-positive cells could be found near blood vessels and their number decreased sharply over time. Masson's trichrome showed that collagen was the dominant component of the chamber content at early stage and was replaced by newly formed small adipocytes over time. Our findings suggested that the TEC implantation could promote the proliferation of adipose precursor cells derived from local adipose tissue, increase angiogenesis, and finally lead to spontaneous adipogenesis by inducing aseptic inflammation and changing local mechanotransduction.

Award winner for outstanding research in the PhD category, 2014 Society for Biomaterials annual meeting and exposition, Denver, Colorado, April 16-19, 2014: Decellularized adipose matrix hydrogels stimulate in vivo neovascularization and adipose formation

Decellularization of tissues offers the ability to produce tissue-specific extracellular matrix (ECM) scaffolds that recreate many of the biochemical aspects of the tissue of interest. In this study, we describe the in vivo function of decellularized adipose ECM hydrogels for treating subcutaneous adipose deficits. Adipose ECM hydrogels were combined with either adipose-derived adult stem cells or a biocompatible cross-linker, injected subcutaneously into nude mice, and evaluated over the course of 1 month. These ECM hydrogels showed improved integration with the surrounding tissue in vivo compared to a clinical standard soft tissue filler, Juvederm, and stimulated neovascularization. More importantly, these adipose ECM hydrogels facilitated new adipose regeneration within the material at 1 month, a feature not seen with current clinical soft tissue fillers. These results contribute to the growing evidence that ECM-based materials are capable of stimulating subcutaneous adipose regeneration, suggesting that future soft tissue filler materials could incorporate ECM elements in order to restore function to adipose deficits instead of simply filling them with static materials.

Adipose-derived stem cells: methods for isolation and applications for clinical use

Adipose tissue sciences have rapidly expanded since the identification of regenerative cells contained within the stromal vascular fraction (SVF) of fat. Isolation of the SVF, containing adipose-derived stem cells (ADSC), can be accomplished efficiently in the operating room or in the laboratory through enzymatic digestion of the adipose tissue and concentration of SVF. Cells can be directly re-injected as a mesotherapeutic agent, recombined with a tissue scaffold (e.g., cell-enriched fat grafts) or expanded in culture for tissue-engineered cell therapeutics. The potential for cell therapy is under current investigation by researchers around the world. This chapter reviews laboratory methods for isolating ADSCs and the ongoing clinical trials evaluating cell therapeutic efficacy across many specialties, including cardiology, neurology, immunology, tissue engineering, sports medicine, and plastic and reconstructive surgery.

Macrophages play a key role in angiogenesis and adipogenesis in a mouse tissue engineering model

We have previously described a mouse adipose tissue engineering model using a silicon chamber enclosing the superficial epigastric pedicle in a Matrigel based environment. We have shown that when Zymosan, a sterile inflammatory agent, is added to the chamber, angiogenesis and adipogenesis are significantly improved. As Zymosan interacts with toll-like receptors on macrophages, the role of macrophages in new tissue development in the tissue engineering chamber was assessed. Morphological and histological results showed that macrophages were presenting in high numbers at 2 weeks but had decreased significantly by 4 and 6 weeks in the chamber. Numerous immature new blood vessels had formed by 2 weeks, becoming more mature at 4 and 6 weeks. Immature adipocytes were visualized at 4 weeks and mature cells, at 6 weeks. To investigate the functional role of macrophages in the tissue engineering process, we knocked out the local macrophage population by inserting Clodronate liposomes in this chamber. This study shows for the first time that when macrophages are depleted, there is minimal new vascular and adipose tissue development. We propose a new theory for tissue engineering in which macrophages play a central role in both neovascularisation and adipogenesis.

Preparation of an adipogenic hydrogel from subcutaneous adipose tissue

The ability to generate controlled amounts of adipose tissue would greatly ease the burden on hospitals for reconstructive surgery. We have previously shown that a tissue engineering chamber containing a vascular pedicle was capable of forming new fat; however, further refinements are required to enhance fat formation. The development and maintenance of engineered adipose tissue requires a suitable source of growth factors and a suitable scaffold. A hydrogel derived from adipose tissue may fulfil this need. Subcutaneous fat was processed into a thermosensitive hydrogel we refer to as adipose-derived matrix (ADM). Protein analysis revealed high levels of basement membrane proteins, collagens and detectable levels of growth factors. Adipose-derived stem cells exposed to this hydrogel differentiated into adipocytes with >90% efficiency and in vivo testing in rats showed significant signs of adipogenesis after 8 weeks. ADM's adipogenic properties combined with its simple gelation, relatively long shelf life and its tolerance to multiple freeze-thaw cycles, makes it a promising candidate for adipose engineering applications.

An adipoinductive role of inflammation in adipose tissue engineering: key factors in the early development of engineered soft tissues

Tissue engineering and cell implantation therapies are gaining popularity because of their potential to repair and regenerate tissues and organs. To investigate the role of inflammatory cytokines in new tissue development in engineered tissues, we have characterized the nature and timing of cell populations forming new adipose tissue in a mouse tissue engineering chamber (TEC) and characterized the gene and protein expression of cytokines in the newly developing tissues. EGFP-labeled bone marrow transplant mice and MacGreen mice were implanted with TEC for periods ranging from 0.5 days to 6 weeks. Tissues were collected at various time points and assessed for cytokine expression through ELISA and mRNA analysis or labeled for specific cell populations in the TEC. Macrophage-derived factors, such as monocyte chemotactic protein-1 (MCP-1), appear to induce adipogenesis by recruiting macrophages and bone marrow-derived precursor cells to the TEC at early time points, with a second wave of nonbone marrow-derived progenitors. Gene expression analysis suggests that TNFα, LCN-2, and Interleukin 1β are important in early stages of neo-adipogenesis. Increasing platelet-derived growth factor and vascular endothelial cell growth factor expression at early time points correlates with preadipocyte proliferation and induction of angiogenesis. This study provides new information about key elements that are involved in early development of new adipose tissue.

The nitric oxide system--cure for shortcomings in adipose tissue engineering?

Adipose tissue engineering aims to grow fat tissue for soft tissue reconstruction after tumour resection or trauma. However, insufficient progenitor cell differentiation and poor vascularization compromise the generation of clinically applicable adipose tissue. The desired process of neo-adipogenesis seems to be difficult to mimic, even though it takes place in all of us, inevitably and rapidly, as soon as we start consuming high-caloric diets. It has previously been proposed that inflammation and its key regulator, nitric oxide (NO), may play a relevant part in neo-adipogenesis. We here discuss how a controlled activation of the nitric oxide system on various levels may represent a cure for several current shortcomings in adipose tissue engineering.

A novel xenograft model with intrinsic vascularisation for growing undifferentiated pleomorphic sarcoma NOS in mice

PURPOSE

Preclinical development of antisarcoma therapy is primarily based on the subcutaneous transplantation of sarcoma xenografts. Tumour cell survival remains a hurdle of current models, which has been attributed to the hypoxic conditions following transplantation. We hypothesised that sarcoma models with an intrinsic tissue-engineered vascular supply are easily reproducible. The aim of this study was to establish a novel vascularised xenograft model.

MATERIALS AND METHODS

Primary human soft tissue sarcomas were transplanted into a silicon chamber and placed around the superficial epigastric vessels of nude mice. Sarcoma xenograft samples were assessed histomorphologically.

RESULTS

All sarcoma xenografts engrafted, leading to solid tumours. Histological, immunohistochemical staining and light/electron microscopy confirmed the xenografts as identical high-grade pleomorphic sarcomas (NOS) compared with the original patients' tumours.

CONCLUSION

This novel sarcoma xenograft model with an intrinsic vascular supply could be of high value for studying human soft tissue sarcomas and their therapy.

The Vascularised Groin Chamber: A Novel Model for Growing Primary Human Liposarcoma in Nude Mice

Background

The preclinical development of anti-sarcoma drugs has been primarily based on the subcutaneous transplantation of xenografts. Transplant survival remains an obstacle of current models which has been attributed to the period of hypoxia after transplantation. We hypothesized that primary soft tissue sarcoma models with an intrinsic tissue engineered vascular supply would be easily reproducible. The aim of this study was to establish a model of primary human soft tissue sarcoma with an intrinsic vascular supply.

Methods

Primary soft tissue sarcoma cells from resected human liposarcomas isolated and divided into tumour fragments were transplanted into a silicon chamber, placed around the superficial epigastric vessels in mice. Sarcoma xenograft samples were analysed histomorphologically (light/electron microscopy and immunohistochemistry).

Results

All primary soft tissue sarcoma transplants engrafted, leading to solid tumours within 3 weeks. Histological and immunohistochemical staining confirmed the mouse xenografts as identical high grade liposarcomas compared to original tumour tissue.

Conclusion

This study established a reproducible xenograft model of primary human liposarcoma. This animal model could be of high value for studying human soft tissue sarcomas and their therapy.

Drug delivery in soft tissue engineering

INTRODUCTION

Tissue defects, sustained through disease or trauma, present enormous challenges in regenerative medicine. Modern tissue engineering (TE) aims at replacing or repairing these defects through a combined approach of biodegradable scaffolds, suitable cell sources and appropriate environmental cues, such as biomolecules presented on scaffold surfaces or sustainably released from within.

AREAS COVERED

This review provides a brief overview of the various drugs and bioactive molecules of interest to TE, as well as a selection of materials that have been proposed for TE scaffolds and matrices in the past. It then proceeds to discuss encapsulation, immobilization and controlled release strategies for bioactive proteins, before discussing recent advances in this area with a special focus on soft TE.

EXPERT OPINION

Overall, minimal clinical success has been achieved so far in using growth factor, morphogen, or adhesion factor modified scaffolds and matrices; only one growth factor delivery system (Regranex Gel), has been approved by the FDA for clinical use, with only a handful of other growth factors being approved for human use so far. However, many more growth factors are currently in clinical Phase I - II or preclinical trials and many delivery systems utilize materials already approved by the FDA for other purposes. With respect to drug delivery in soft TE, a combination of increased research efforts in hydrogel and support material development as well as growth factor development is needed before clinical success is realized.

Nitric oxide and downstream second messenger cGMP and cAMP enhance adipogenesis in primary human preadipocytes

BACKGROUND AIMS

Obesity is correlated with chronic low-grade inflammation. Thus the induction of inflammation could be used to stimulate adipose tissue formation in tissue-engineering approaches. As nitric oxide (NO) is a key regulator of inflammation, we investigated the effect of NO and its downstream signaling molecule guanosine 3',5'-cyclic monophosphate (cGMP) as well as adenosine 3',5'-cyclic monophosphate (cAMP) on preadipocytes in vitro.

METHODS

Preadipocytes were isolated from human subcutaneous adipose tissue, cultured until confluence, and differentiated. The NO donor diethylenetriamine (DETA)/NO (30-150 microm) was added during proliferation and differentiation. Additionally, cGMP/cAMP analogs 8-bromoguanosine 3',5'-cyclic monophosphate (8-Br-cGMP), 8-(4-chlorophenylthio)-guanosine 3',5'-cyclic monophosphate (8-pCPT-cGMP) and 8-bromoadenosine 3',5'-cyclic monophosphate (8-Br-cAMP), and the adenylyl cyclase activator forskolin, specific guanylyl cyclase inhibitor 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (ODQ) and adenylyl cyclase inhibitor 2'-5'-dideoxyadenosine (ddA), were applied. Proliferation and differentiation were evaluated.

RESULTS

DETA/NO in combination with the standard differentiation procedure significantly enhanced maturation of precursor cells to adipocytes. Proliferation, in contrast, was inhibited in the presence of NO. The application of cGMP and cAMP, respectively, increased pre-adipocyte differentiation to an even higher extent than NO. Inhibitors of the underlying pathways caused a significant decrease in adipogenic conversion.

CONCLUSIONS

Our results support the application of NO donors during transplantation of preadipocytes in a 3-dimensional setting to accelerate and optimize differentiation. The results suggest that, instead of the rather instable and reactive molecule NO, the application of cGMP and cAMP would be even more effective because these substances have a stronger adipogenic effect on preadipocytes and a longer half-life than NO. Also, by applying inhibitors of the underlying pathways, the induced inflammatory condition could be regulated to the desired level.