Activated omentum becomes rich in factors that promote healing and tissue regeneration

Omentopexy versus no omentopexy in sleeve gastrectomy: an updated systematic review and meta-analysis

Laparoscopic sleeve gastrectomy with omentopexy (O-LSG) has been compared to laparoscopic sleeve gastrectomy with no-omentopexy (NO-LSG) in terms of postoperative outcomes and one-year anthropometric results. This systematic review with meta-analysis aimed to compare the utility of omentopexy in sleeve gastrectomy. We performed a systematic review with meta-analysis according to PRISMA 2020 and AMSTAR 2 guidelines. We included studies that systematically searched electronic databases and compared the O-LSG with the NO-LSG conducted through 1st March 2023. The bibliographic research yielded 13 eligible studies. These studies included 5514 patients. The O-LSG is associated with lower leakage (OR = 0.22; 95% CI [0.08, 0.55], p = 0.001), bleeding (OR = 0.33; 95% CI [0.19, 0.57], p < 0.0001), vomiting (OR = 0.50; 95% CI [0.28, 0.89], p = 0.02), twist (OR = 0.09; 95% CI [0.02, 0.39], p = 0.001), and shorter hospital stay (MD = - 0.33; 95% CI [- 0.61, - 0.05], p = 0.02) compared with NO-LSG. The O-LSG is associated with longer operative time (MD = 8.15; 95% CI [3.65, 12.64], p = 0.0004) than the NO-LSG. There were no differences between the two groups in terms of postoperative GERD (OR = 0.53; 95% CI [0.27, 1.02], p = 0.06), readmission (OR = 0.60; 95% CI [0.27, 1.37], p = 0.23), and one-year total weight loss (MD = 2.06; 95% CI [- 1.53, 5.65], p = 0.26). In the subgroup analysis including only RCTs, postoperative GERD was lower in the O-LSG (OR = 0.26; 95% CI [0.11, 0.63], p = 0.003). Our systematic review and meta-analysis concluded that omentopexy in sleeve gastrectomy is feasible and safe It reduced leakage, bleeding, and twist. It probably increased the operative time. It may reduce vomiting, GERD, and hospital stay. We don't know if it led to an additional readmission rate or one-year total weight loss.Registration The protocol was registered in PROSPERO with the ID CRD42022336790.

Identifying the Morphological and Molecular Features of a Cell-Based Orthotopic Pancreatic Cancer Mouse Model during Growth over Time

Pancreatic ductal adenocarcinoma (PDAC), characterized by hypovascularity, hypoxia, and desmoplastic stroma is one of the deadliest malignancies in humans, with a 5-year survival rate of only 7%. The anatomical location of the pancreas and lack of symptoms in patients with early onset of disease accounts for late diagnosis. Consequently, 85% of patients present with non-resectable, locally advanced, or advanced metastatic disease at diagnosis and rely on alternative therapies such as chemotherapy, immunotherapy, and others. The response to these therapies highly depends on the stage of disease at the start of therapy. It is, therefore, vital to consider the stages of PDAC models in preclinical studies when testing new therapeutics and treatment modalities. We report a standardized induction of cell-based orthotopic pancreatic cancer models in mice and the identification of vital features of their progression by ultrasound imaging and histological analysis of the level of pancreatic stellate cells, mature fibroblasts, and collagen. The results highlight that early-stage primary tumors are secluded in the pancreas and advance towards infiltrating the omentum at week 5-7 post implantation of the BxPC-3 and Panc-1 models investigated. Late stages show extensive growth, the infiltration of the omentum and/or stomach wall, metastases, augmented fibroblasts, and collagen levels. The findings can serve as suggestions for defining growth parameter-based stages of orthotopic pancreatic cancer models for the preclinical testing of drug efficacy in the future.

Laparoscopically harvested omental flap for immediate breast reconstruction: a retrospective single-center study of 300 cases

BACKGROUND

The laparoscopically harvested omental flap (LHOF) has been used in partial or total breast reconstruction, but most studies on LHOF were case reports or small case series. However, the clinical feasibility and oncological safety of LHOF in oncoplastic breast surgery remains controversial. This study reported our experience applying LHOF for immediate breast reconstruction.

METHODS

Between June 2018 and March 2022, 300 patients underwent oncoplastic breast surgery using LHOF at our institution. Their clinicopathological data, complications, cosmetic outcomes, and oncologic outcomes were evaluated.

RESULTS

All patients underwent total breast reconstruction using LHOF after nipple-sparing mastectomy. The median operation time was 230 min (ranging from 155 to 375 min). The median operation time for harvesting the omental flap was 55 min (ranging from 40 to 105 min). The success rate of the laparoscopically harvested pedicled omental flap was over 99.0%. Median blood loss was 70 ml, ranging from 40 to 150 ml. The volume of the flap was insufficient in 102 patients (34.0%). The overall complication rate was 12.3%. Subcutaneous fluid in the breast area (7%) was the most common reconstruction-associated complication, but most cases were relieved spontaneously. The incidence rate of omental flap necrosis was 3.3%. LHOF-associated complications occurred in two cases, including one case of incisional hernia and one case of vascular injury. Cosmetic outcomes were satisfactory in 95.1% of patients on a four-point scale by three-panel assessment and 97.2% using the BCCT.core software. Two local and one systemic recurrence were observed during a median follow-up period of 32 months.

CONCLUSIONS

The LHOF for immediate breast reconstruction is a safe and feasible method that involves minimal donor-site morbidity, satisfactory cosmetic outcomes, and promising oncologic safety.

Skeletal muscle niche, at the crossroad of cell/cell communications

Skeletal muscle is composed of a variety of tissue and non-tissue resident cells that participate in homeostasis. In particular, the muscle stem cell niche is a dynamic system, requiring direct and indirect communications between cells, involving local and remote cues. Interactions within the niche must happen in a timely manner for the maintenance or recovery of the homeostatic niche. For instance, after an injury, pro-myogenic cues delivered too early will impact on muscle stem cell proliferation, delaying the repair process. Within the niche, myofibers, endothelial cells, perivascular cells (pericytes, smooth muscle cells), fibro-adipogenic progenitors, fibroblasts, and immune cells are in close proximity with each other. Each cell behavior, membrane profile, and secretome can interfere with muscle stem cell fate and skeletal muscle regeneration. On top of that, the muscle stem cell niche can also be modified by extra-muscle (remote) cues, as other tissues may act on muscle regeneration via the production of circulating factors or the delivery of cells. In this review, we highlight recent publications evidencing both local and remote effectors of the muscle stem cell niche.

Omental coating attenuates implant-induced foreign body reaction in rats

The objective of this study is to clarify whether the omental coating can effectively attenuate foreign body reaction (FBR) induced by implanted materials. Male Sprague-Dawley rats were injected with polydextran particle slurry intraperitoneally to activate the omentum. 7 days later, polyether polyurethane sponge discs were implanted subcutaneously on each side of the rat's back as the foreign implants to induce FBR. The next day, omental transposition were performed. The disc on the left side of each rat's back was wrapped with omental flap (omental group); the disc on the right side was untreated (control group). All discs were removed 21 days after implantation and assessed by determining the components of the fibrovascular tissue (angiogenesis, inflammation, foreign body giant cells (FBGCs) aggregation and fibrogenesis). In implants in omental group, micro vessel density (MVD), Hemoglobin (Hb) content and VEGF levels (pro-angiogenic cytokine) were increased when compared with implants from control group. Inflammatory parameters (IL-1β; macrophage accumulation-NAG activity; neutrophil accumulation- MPO levels) were decreased in implants after omental coating. Also, collagen deposition, fibrous capsule thickness, and FBGCs decreased in implants from omental group. However, intra-implant levels of TNF-α and TGF-β1 were not different after omental coating. Our findings showed for the first time that the omental coating around the implants attenuate the adverse FBR, it may be critical in developing new strategies to control FBR and improve the function and performance of the implanted materials.

Robotic omentectomy in gynecologic oncology: surgical anatomy, indications, and a technical approach

An omentectomy is a standard component care of gynecological cancers, particularly for surgical staging and treatment for malignant ovarian neoplasms, borderline tumors, fallopian tube cancers, primary peritoneal cancers as well as certain histological subtypes of endometrial cancer. Traditionally, an omentectomy is performed by an open laparotomy approach, however, use of a robotic approach has gained popularity and has been proven to be both safe and effective. In spite of the advantages of robotic surgery compared to laparotomy, the inherent technical challenges of a robotic omentectomy may limit its uptake. In this article, we review (1) the physiology and surgical anatomy of the omentum, (2) the role of the omentum in immune regulation and oncogenesis, (3) indications for an omentectomy in the setting of gynecological malignancy, and (4) describe a step-by-step 3-arm technique for performing both a infracolic and gastrocolic omentectomy procedure using a robotic approach.

Bacterial Cellulose-Based Materials: A Perspective on Cardiovascular Tissue Engineering Applications

Today, a wide variety of bio- and nanomaterials have been deployed for cardiovascular tissue engineering (TE), including polymers, metal oxides, graphene/its derivatives, organometallic complexes/composites based on inorganic-organic components, among others. Despite several advantages of these materials with unique mechanical, biological, and electrical properties, some challenges still remain pertaining to their biocompatibility, cytocompatibility, and possible risk factors (e.g., teratogenicity or carcinogenicity), restricting their future clinical applications. Natural polysaccharide- and protein-based (nano)structures with the benefits of biocompatibility, sustainability, biodegradability, and versatility have been exploited in the field of cardiovascular TE focusing on targeted drug delivery, vascular grafts, engineered cardiac muscle, etc. The usage of these natural biomaterials and their residues offers several advantages in terms of environmental aspects such as alleviating emission of greenhouse gases as well as the production of energy as a biomass consumption output. In TE, the development of biodegradable and biocompatible scaffolds with potentially three-dimensional structures, high porosity, and suitable cellular attachment/adhesion still needs to be comprehensively studied. In this context, bacterial cellulose (BC) with high purity, porosity, crystallinity, unique mechanical properties, biocompatibility, high water retention, and excellent elasticity can be considered as promising candidate for cardiovascular TE. However, several challenges/limitations regarding the absence of antimicrobial factors and degradability along with the low yield of production and extensive cultivation times (in large-scale production) still need to be resolved using suitable hybridization/modification strategies and optimization of conditions. The biocompatibility and bioactivity of BC-based materials along with their thermal, mechanical, and chemical stability are crucial aspects in designing TE scaffolds. Herein, cardiovascular TE applications of BC-based materials are deliberated, with a focus on the most recent advancements, important challenges, and future perspectives. Other biomaterials with cardiovascular TE applications and important roles of green nanotechnology in this field of science are covered to better compare and comprehensively review the subject. The application of BC-based materials and the collective roles of such biomaterials in the assembly of sustainable and natural-based scaffolds for cardiovascular TE are discussed.

Bioengineered omental transplant site promotes pancreatic islet allografts survival in non-human primates

The transplanting islets to the liver approach suffers from an immediate posttransplant loss of islets of more than 50%, progressive graft dysfunction over time, and precludes recovery of grafts should there be serious complications such as the development of teratomas with grafts that are stem cell-derived islets (SC-islets). The omentum features an attractive extrahepatic alternative site for clinical islet transplantation. We explore an approach in which allogeneic islets are transplanted onto the omentum, which is bioengineered with a plasma-thrombin biodegradable matrix in three diabetic non-human primates (NHPs). Within 1 week posttransplant, each transplanted NHP achieves normoglycemia and insulin independence and remains stable until termination of the experiment. Success was achieved in each case with islets recovered from a single NHP donor. Histology demonstrates robust revascularization and reinnervation of the graft. This preclinical study can inform the development of strategies for β cell replacement including the use of SC-islets or other types of novel cells in clinical settings.

Co-transplantation with mesenchymal stem cells and endothelial cells improvise islet engraftment and survival in STZ treated hyperglycemic mice

Though intra-portal islet transplantation demonstrated as best suited strategy for the reversal of hyperglycemia without the threat of iatrogenic hyperglycemia in type 1 diabetes (T1D) in patients, the inferior quality of post-transplantation (tx) vascularization needs to be addressed for the maximization of post-tx islet survival. Therefore, in this study, we have first generated MSCs and endothelial progenitor cells (EPC) from mice bone marrow by in house optimized protocol and then 3-D co-cultured them with mice islets. Secretion of in the culture supernatant suggested the pro-angiogenic nature of 3D cultured mice islets. After 5 days post-tx of these pro-angiogenic islets in the omental pouch of syngeneic mice led to: 1) restoration of normoglycemia, 2) secretion of mouse C-peptide and 3) induction of angiogenic factors after 3 days of post-tx. The induction of angiogenic factors was done by RT-qPCR of omental biopsies. Importantly, pro-angiogenic islet recipient mice also demonstrated the clearance of glucose within 75 min, reflecting their efficient function and engraftment. Our results highlights needs of 3-D co-culture islets for superior quality post-tx islet vasculature and better engraftment â€" crux to improvise the challenges associated with post-tx islet vascularization and functions.

Comparison of Omentum and Subcutis as Implant Sites for Device-Encapsulated Human iPSC-Derived Pancreatic Endoderm in Nude Rats

Subcutaneous implants of device-encapsulated stem cell-derived pancreatic endoderm (PE) can establish a functional beta cell mass (FBM) with metabolic control in immune-compromised mice. In a study with human-induced pluripotent stem cell-PE, this outcome was favored by a preformed pouch which allowed lesion-free insertion of devices in a pre-vascularized site. This was not reproduced in nude rats, known to exhibit a higher innate reactivity than mice and therefore relevant as preclinical model: a dense fibrotic capsule formed around subcutis (SC) implants with virtually no FBM formation. Placement in omentum (OM) of nude rats provided a less fibrous, better vascularized environment than SC. It resulted in less donor cell loss (56% recovery at post-transplant-PT week 3 versus 16% in SC) allowing FBM-formation. At PT week 30, 6/13 OM-recipients exhibited glucose-induced plasma hu-C-peptide to 0.1-0.4 ng/ml, versus 0/8 in SC-recipients. These levels are more than 10-fold lower than in a state of metabolic control. This shortcoming is not caused by inadequate glucose responsiveness of the beta cells but by their insufficient number. The size of the formed beta cell mass (0.4 ± 0.2 µl) was lower than that reported in mice receiving the same cell product subcutaneously; the difference is attributed to a lower expansion of pancreatic progenitor cells and to their lower degree of differentiation to beta cells. This study in the nude rat model demonstrates that OM provides a better environment for formation of beta cells in device-encapsulated PE-implants than SC. It also identified targets for increasing their dose-efficacy.

Free omental graft without vascular microanastomosis in the cutaneous wound healing of rabbits

ABSTRACT This study aims to evaluate the influence of free omental graft without vascular microanastomosis (FOGWVA) on experimental skin healing in rabbits. Through celiotomy, a 9cm2 free omental fragment was collected in 36 rabbits, with subsequent production of a deep linear cutaneous wound in the dorsal midline measuring 3cm. In 18 animals from the omental group (OG), the omental fragment collected was fixed subcutaneously with six simple interrupted stitches using a 4-0 polyamide thread. In both treated and control (CG) groups, intradermal dermorrhaphy was performed with 4-0 polyamide thread. Experimental wounds were clinically evaluated every day. Each of the groups was divided into three subgroups of 6 animals each for histopathological evaluation on the 7th, 14th, and 28th days of postoperative. In the OG wounds, the increase in volume (omentum activation) stood out after the second postoperative day. Macroscopy showed an organic reaction to the graft on day 7, with a progressive reduction in addition to neovascularization towards the omental graft. The intense presence of mononuclear cells and collagen deposition on day 7 demonstrated an accelerated process of tissue remodeling and repair. The FOGWVA omental graft remained viable and positively influenced the cutaneous healing of the experimental wounds in rabbits.

Cardio-omentopexy requires a cardioprotective innate immune response to promote myocardial angiogenesis in mice

Objective

The pedicled greater omentum, when applied onto stressed hearts using omentopexy, has been shown to be protective in humans and animals. The mechanisms underlying cardioprotection using omentopexy remain elusive. This study examined whether macrophage-mediated angiogenesis accounts for the cardioprotective effect of omentopexy in mice.

Methods

C57BL/6 mice were subjected to minimally invasive transverse aortic constriction for 6 weeks and subsequent cardio-omentopexy for 8 weeks. Control mice underwent the same surgical procedures without aortic constriction or cardio-omentopexy.

Results

Transverse aortic constriction led to left ventricular concentric hypertrophy, reduced mitral E/A ratio, increased cardiomyocyte size, and myocardial fibrosis in the mice that underwent sham cardio-omentopexy surgery. The negative effects of transverse aortic constriction were prevented by cardio-omentopexy. Myocardial microvessel density was elevated in the mice that underwent aortic constriction and sham cardio-omentopexy surgery, and cardio-omentopexy further enhanced angiogenesis. Nanostring gene array analysis uncovered the activation of angiogenesis gene networks by cardio-omentopexy. Flow cytometric analysis revealed that cardio-omentopexy triggered the accumulation of cardiac MHCIIloLyve1+TimD4+ (Major histocompatibility complex class IIlow lymphatic vessel endothelial hyaluronan receptor 1+ T cell immunoglobulin and mucin domain conataining 4+) resident macrophages at the omental-cardiac interface. Intriguingly, the depletion of macrophages with clodronate-liposome resulted in the failure of cardio-omentopexy to protect the heart and promote angiogenesis.

Conclusions

Cardio-omentopexy protects the heart from pressure overload-elicited left ventricular hypertrophy and dysfunction by promoting myocardial angiogenesis. Cardiac MHCIIloLyve1+TimD4+ resident macrophages play a critical role in the cardioprotective effect and angiogenesis of cardio-omentopexy.

Video Abstract

Postoperative bronchopleural fistula repair: Surgical outcomes and adverse factors for its success

BACKGROUND

The purpose of this study was to investigate the results of postoperative bronchopleural fistula repair and to identify adverse factors for its success.

METHODS

We retrospectively reviewed the surgical results of 39 patients who underwent surgical repair for postoperative bronchopleural fistula between January 2010 and June 2020. Success of bronchopleural fistula repair was defined as the visual closure of the bronchopleural fistula with the absence of an air leak, a recurrence of bronchopleural fistula and infection in the thoracic cavity.

RESULTS

Twenty-five (64.1%) bronchopleural fistulas occurred after pulmonary resection and 14 (35.9%) after lung transplantation. Bronchopleural fistula was diagnosed 19 days (median) and repaired 28 days (median) after the initial operation by primary closure in 27 (69.2%) patients, and by additional resection in 12 (30.8%) patients. The overall success rate was 59% (23/39) and the overall mortality was 56.4% (22/39). Multivariable analysis revealed that the patients who were supported by mechanical ventilation at the time of repair had significantly lower success rates than those without (15.4%, 2/13 vs. 80.8%, 21/26, respectively, p < 0.001). The omental flap group tended to have a better success rate than the muscle flap group (p = 0.07).

CONCLUSIONS

There was a high overall mortality rate after bronchopleural fistula repair and a low success rate. Mechanical ventilation at the time of bronchopleural fistula repair was significantly related to the failure of bronchopleural fistula repair.

Heterogeneity of Adipose Stromal Vascular Fraction Cells from the Different Harvesting Sites in Rats

In both veterinary and human health, regenerative medicine offers a promising cure for various disorders. One of the rate-limiting challenges in regenerative medicine is the considerable time and technique required to expand and grow cells in culture. Therefore, the stromal vascular fraction (SVF) shows a significant promise for various cell therapy approaches. The present study aimed to define and investigate the optimal harvest site of freshly isolated SVF cells from various adipose tissue (AT) depot sites in the female Sprague-Dawley (S.D.) rat. First, Hematoxylin and eosin (H&E) were used to analyze the morphological variations in AT samples from peri-ovarian, peri-renal, mesenteric, and omental sites. The presence of putative stromal cells positive CD34 was detected using immunohistochemistry. Then, the isolated SVF cells were examined for cell viability and cellular yield differences. Finally, the expression of mesenchymal stem cells and hematopoietic markers in the SVF cells subpopulation was studied using flow cytometry. The pluripotent gene expression profile was also evaluated. CD34 staining of the omental AT was substantially higher than those of other anatomical sites. Despite having the least quantity of fat, omental AT has the highest SVF cell fraction and viable cells. Along with CD90 and CD44 higher expression, Oct4, Sox2, and Rex-1 genes levels were higher in SVF cells isolated from the omental AT. To conclude, omental fat is the best candidate for SVF cell isolation in female S.D. rats with the highest SVF cell fraction with higher MSCs phenotypes and pluripotency gene expression.

Autologous omentum transposition for regeneration of a renal injury model in rats

BACKGROUND

After renal trauma, surgical treatment is vital, but sometimes there may be loss of function due to fibrosis. This study aimed to evaluate the effect of autologous omentum flaps on injured renal tissues in a rat model.

METHODS

A total of 30 Wistar albino rats were included and randomly divided equally into a control group and four intervention groups. Iatrogenic renal injuries were repaired using a surgical technique (primary repair 1 group and primary repair 2 group) or transposition of the autologous omentum (omentum repair 1 group and omentum repair 2 group). Blood samples were taken preoperatively and on the 1st and 7th postoperative days in all groups and on the 18th postoperative day in the control and two intervention groups. All rats were sacrificed on the 7th or 18th day postoperatively, and their right kidneys were taken for histopathological evaluation.

RESULTS

The mean urea level significantly decreased from day 1 to day 7 and from day 1 to day 18 in the omentum repair 2 group (P = 0.005 and P = 0.004, respectively). There were no other significant changes in urea or creatinine levels within the intervention groups (P > 0.05). There was no significant correlation between the urea and creatinine levels and the histological scores (P > 0.05). The primary repair 1 and 2 groups had significantly higher median granulation and inflammation scores in the kidney specimen than the control and omentum repair groups (P < 0.05). The omentum repair 2 group had significantly lower median granulation and inflammation scores in the surrounding tissues than the primary repair 2 group (P < 0.05). The completion score for the healing process in the kidney specimen was significantly higher in the omentum repair groups than in the primary repair groups (P < 0.05). The omentum repair 2 group had significantly lower median granulation and inflammation scores in the surrounding tissues than the primary repair 2 group (P < 0.05). Granulation degree in the kidney specimen was strongly and positively correlated with the inflammation degree (r = 0.824, P < 0.001) and foreign body reaction in the kidney specimen (r = 0.872, P < 0.001) and a strong and negative correlation with the healing process completion score in the kidney (r = - 0.627, P = 0.001). Inflammation degree in the kidney specimen was strongly and positively correlated with the foreign body reaction in the kidney specimen (r = 0.731, P = 0.001) and strongly and negatively correlated with the healing process completion score in the kidney specimen (r = - 0.608, P = 0.002).

CONCLUSION

Autologous omentum tissue for kidney injury repair attenuated inflammation and granulation. Additionally, the use of omental tissue to facilitate healing of kidney injury may theoretically lead to a more effective healing process and reduced fibrosis and tissue and function loss.

Successful Postoperative Nephrocutaneous Fistula Treatment With Omental Flap Grafting: A Case Report

Nephrocutaneous fistula (NCF) is a rare and severe complication of renal disease and surgical procedures. Treatments for NCF are based on the renal function, and can include nephrectomy, heminephrectomy, nephroureterectomy, endourological maneuvers or antibiotic therapy alone. Here we report a case of a chronic NCF which occurred 5 years after partial nephrectomy. In this report, we describe a new surgical approach for the management of a patient with postoperative NCF. In the present case, in addition to removing the fistulous tract, we also performed an omental flap grafting to tightly cover the kidney. In addition to limiting and controlling the local inflammation, the omental flap prevents contact between the kidney and the flank muscle on its posterior rim. No recurrence or complications occurred throughout 10 months of follow-up. The NCF was successfully treated with completely removal of the sinus tract and omental flap grafting, without nephrectomy. This case adds new aspects to the treatment of NCF.

Prevention, Diagnosis and Management of Post-Surgical Mediastinitis in Adults Consensus Guidelines of the Spanish Society of Cardiovascular Infections (SEICAV), the Spanish Society of Thoracic and Cardiovascular Surgery (SECTCV) and the Biomedical Research Centre Network for Respiratory Diseases (CIBERES)

This is a consensus document of the Spanish Society of Cardiovascular Infections (SEICAV), the Spanish Society of Thoracic and Cardiovascular Surgery (SECTCV) and the Biomedical Research Centre Network for Respiratory Diseases (CIBERES). These three entities have brought together a multidisciplinary group of experts that includes anaesthesiologists, cardiac and cardiothoracic surgeons, clinical microbiologists, infectious diseases and intensive care specialists, internal medicine doctors and radiologists. Despite the clinical and economic consequences of sternal wound infections, to date, there are no specific guidelines for the prevention, diagnosis and management of mediastinitis based on a multidisciplinary consensus. The purpose of the present document is to provide evidence-based guidance on the most effective diagnosis and management of patients who have experienced or are at risk of developing a post-surgical mediastinitis infection in order to optimise patient outcomes and the process of care. The intended users of the document are health care providers who help patients make decisions regarding their treatment, aiming to optimise the benefits and minimise any harm as well as the workload.

Expression of Antimicrobial Peptides and Cytokines in Human Omentum Following Abdominal Surgery

Introduction

Omentum can secrete out biological agents like different growth factors, cytokines, and antimicrobial peptides. The aim of our study was to determine the expression of antimicrobial peptides and cytokines in human omentum tissue and its response to intra-abdominal infection.

Methodology

Omentum tissue was obtained from 60 patients: control (n=20) and cases (n=40). mRNA expression of antimicrobial peptides (LL-37, HBD-1, HBD-2, HNP1-3) and cytokines (TNF- α, IL-8, IL-10, IL1β) was evaluated using Real-Time PCR. Protein quantification was done by Immunoblotting and ELISA.

Results

Significantly higher expression of antimicrobial peptides (LL-37, HBD-1, HBD-2, HNP1-3) and cytokines (TNF- α, IL-8, IL-10, IL1β) was observed in cases as compared to control at both the transcriptional and translational level (p<0.0001).

Conclusion

Omentum governs a population of antimicrobial peptides with potent immunologic functions. The expression of antimicrobial peptides and cytokines is inducible and increases with the severity of infection. Omentum is thus an immunologically active and adaptable organ but its complete regulatory mechanism is still elusive.

Autologous Activated Omental versus Allogeneic Adipose Tissue-Derived Mesenchymal Stem Cells in Corneal Alkaline Injury: An Experimental Study

Purpose:

To compare the effects of two types of mesenchymal stem cells (MSCs), activated omental cells (AOCs), and adipose tissue-derived stem cells (ADSCs) in the healing process of animal model of ocular surface alkali injury.

Methods:

An alkaline burn was induced on the ocular surfaces of eighteen rats divided randomly into three groups. The first and second groups received subconjunctival AOCs and ADSCs, respectively. The control group received normal saline subconjunctival injection. On the 90^th day after the injury, the eyes were examined using slit-lamp biomicroscopy. Corneal neovascularization and scarring were graded in a masked fashion. Histological evaluation of the corneal scar was performed, and the number of inflammatory cells was evaluated.

Results:

Corneal neovascularization scores revealed higher neovascularization in the control (0.49 ± 0.12) than the AOC (0.80 ± 0.20, P = 0.01) and ADSC groups (0.84 ± 0.24, P = 0.007). There were no statistically significant differences between the neovascularization score of the AOC and ADSC groups (P > 0.05). According to histologic evaluation, stromal infiltration was significantly more in the control group compared to AOC and ADSC groups (P < 0.05).

Conclusions:

Our results suggest that MSCs, even with different sources, can be used to promote wound healing after corneal chemical burns. However, the ease of harvesting ADSC from more superficial fat sources makes this method more clinically applicable.

Circumferential esophageal replacement by a decellularized esophageal matrix in a porcine model

BACKGROUND

Tissue engineering is an attractive alternative to conventional esophageal replacement techniques using intra-abdominal organs which are associated with a substantial morbidity. The objective was to evaluate the feasibility of esophageal replacement by an allogenic decellularized esophagus in a porcine model. Secondary objectives were to evaluate the benefit of decellularized esophagus recellularization with autologous bone marrow mesenchymal stromal cells and omental maturation of the decellularized esophagus.

METHODS

Eighteen pigs divided into 4 experimental groups according to mesenchymal stromal cells recellularization and omental maturation underwent a 5-cm long circumferential replacement of the thoracic esophagus. Turbo green florescent protein labelling was used for in vivo mesenchymal stromal cells tracking. The graft area was covered by a stent for 3 months. Clinical and histologic outcomes were analyzed over a 6-month period.

RESULTS

The median follow-up was 112 days [5; 205]. Two animals died during the first postoperative month, 2 experienced an anastomotic leakage, 13 experienced a graft area stenosis following stent migration of which 3 were sacrificed as initially planned after successful endoscopic treatment. The stent could be removed in 2 animals: the graft area showed a continuous mucosa without stenosis. After 3 months, the graft area showed a tissue specific regeneration with a mature epithelium and muscular cells. Clinical and histologic results were similar across experimental groups.

CONCLUSION

Circumferential esophageal replacement by a decellularized esophagus was feasible and allowed tissue remodeling toward an esophageal phenotype. We could not demonstrate any benefit provided by the omental maturation of the decellularized esophagus nor its recellularization with mesenchymal stromal cells.

Potential Role of Diabetes Mellitus-Associated T Cell Senescence in Epithelial Ovarian Cancer Omental Metastasis

Epithelial ovarian cancer (EOC) is one of the most common causes of cancer-related deaths among women and is associated with age and age-related diseases. With increasing evidence of risks associated with metabolic inflammatory conditions, such as obesity and type 2 diabetes mellitus (T2DM), it is important to understand the complex pathophysiological mechanisms underlying cancer progression and metastasis. Age-related conditions can lead to both genotypic and phenotypic immune function alterations, such as induction of senescence, which can contribute to disease progression. Immune senescence is a common phenomenon in the ageing population, which is now known to play a role in multiple diseases, often detrimentally. EOC progression and metastasis, with the highest rates in the 75-79 age group in women, have been shown to be influenced by immune cells within the "milky spots" or immune clusters of the omentum. As T2DM has been reported to cause T cell senescence in both prediabetic and diabetic patients, there is a possibility that poor prognosis in EOC patients with T2DM is partly due to the accumulation of senescent T cells in the omentum. In this review, we explore this hypothesis with recent findings, potential therapeutic approaches, and future directions.

Cellular basis of omentum activation and expansion revealed by single-cell RNA sequencing using a parabiosis model

Although the physiological function of the omentum remains elusive, it has been proposed that it plays an important role in fat storage, immune regulation, and regeneration of injured tissues and organs. Although the omentum undergoes expansion upon activation, reports on the accurate assessment of increased cell types and the origin of the increased cells remain limited. To investigate this aspect, the omenta of parabiotic mice were subjected to activation using distinct fluorescent markers and single-cell RNA sequencing (scRNA-seq) was performed to identify circulation-derived omental cells. We found that a considerable number of circulating cells contributed to the activation of the omentum. The omental cells derived from circulating cells exhibited morphological features similar to those of fibroblasts. scRNA-seq revealed the existence of a novel cell population that co-expressed macrophage and fibroblast markers in the activated omentum, suggesting that it corresponded to circulating macrophage-derived fibroblast-like cells. Lineage tracing experiments revealed that most fibroblasts in the activated omentum were not derived from WT1-positive mesenchymal progenitors. The cell cluster also expressed various chemokine genes, indicating its role in the activation and recruitment of immune cells. These results provide important information regarding the activation of the omentum.

Instruction of Immunometabolism by Adipose Tissue: Implications for Cancer Progression

Simple Summary

Metabolism is the process by which living organisms and cells generate energy to sustain life. At the organismal level, metabolic homeostasis is a tightly controlled balance between energy consumption and energy expenditure. Many studies have shown that disruption of this homeostasis leads to an inflammatory phenotype within adipose tissue. The aim of this review is to provide an overview of the dynamic metabolic interplay within adipose tissue and its implications for cancer progression and metastasis.

Abstract

Disruption of metabolic homeostasis at the organismal level can cause metabolic syndrome associated with obesity. The role of adipose tissue in cancer has been investigated over the last several decades with many studies implicating obesity as a risk factor for the development of cancer. Adipose tissue contains a diverse array of immune cell populations that promote metabolic homeostasis through a tightly controlled balance of pro- and anti-inflammatory signals. During obesity, pro-inflammatory cell types infiltrate and expand within the adipose tissue, exacerbating metabolic dysfunction. Some studies have now shown that the intracellular metabolism of immune cells is also deregulated by the lipid-rich environment in obesity. What is not fully understood, is how this may influence cancer progression, metastasis, and anti-tumor immunity. This review seeks to highlight our current understanding of the effect of adipose tissue on immune cell function and discuss how recent results offer new insight into the role that adipose tissue plays in cancer progression and anti-tumor immunity.

Omentum support for cardiac regeneration in ischaemic cardiomyopathy models: a systematic scoping review

OBJECTIVES

Preclinical in vivo studies using omental tissue as a biomaterial for myocardial regeneration are promising and have not previously been collated. We aimed to evaluate the effects of the omentum as a support for bioengineered tissue therapy for cardiac regeneration in vivo. 

METHODS

A systematic scoping review was performed. Only English-language studies that used bioengineered cardio-regenerative tissue, omentum and ischaemic cardiomyopathy in vivo models were included.

RESULTS

We initially screened 1926 studies of which 17 were included in the final qualitative analysis. Among these, 11 were methodologically comparable and 6 were non-comparable. The use of the omentum improved the engraftment of bioengineered tissue by improving cell retention and reducing infarct size. Vascularization was also improved by the induction of angiogenesis in the transplanted tissue. Omentum-supported bioengineered grafts were associated with enhanced host reverse remodelling and improved haemodynamic measurements.

CONCLUSIONS

The omentum is a promising support for myocardial regenerative bioengineering in vivo. Future studies would benefit from more homogenous methodologies and reporting of outcomes to allow for direct comparison.

Bone tissue engineering in the greater omentum with computer-aided design/computer-aided manufacturing scaffolds is enhanced by a periosteum transplant

Aim: This study aimed to evaluate two different vascularized bone flap scaffolds and the impact of two barrier membranes for the reconstruction of critical-size bone defects. Materials & methods: 3D-printed scaffolds of biodegradable calcium phosphate and bioinert titanium were loaded with rhBMP-2 bone marrow aspirate, wrapped by a collagen membrane or a periosteum transplant and implanted into the greater omentum of miniature pigs. Results: Histological evaluation demonstrated significant bone formation within the first 8 weeks in both scaffolds. The periosteum transplant led to enhanced bone formation and a homogenous distribution in the scaffolds. The omentum tissue grew out a robust vascular supply. Conclusion: Endocultivation using 3D-printed scaffolds in the greater omentum is a very promising approach in defect-specific bone tissue regeneration.

Intraperitoneal Oil Application Causes Local Inflammation with Depletion of Resident Peritoneal Macrophages

Oil is frequently used as a solvent to inject lipophilic substances into the peritoneum of laboratory animals. Although mineral oil causes chronic peritoneal inflammation, little is known whether other oils are better suited. We show that olive, peanut, corn, or mineral oil causes xanthogranulomatous inflammation with depletion of resident peritoneal macrophages. However, there were striking differences in the severity of the inflammatory response. Peanut and mineral oil caused severe chronic inflammation with persistent neutrophil and monocyte recruitment, expansion of the vasculature, and fibrosis. Corn and olive oil provoked no or only mild signs of chronic inflammation. Mechanistically, the vegetal oils were taken up by macrophages leading to foam cell formation and induction of cell death. Olive oil triggered caspase-3 cleavage and apoptosis, which facilitate the resolution of inflammation. Peanut oil and, to a lesser degree, corn oil, triggered caspase-1 activation and macrophage pyroptosis, which impair the resolution of inflammation. As such, intraperitoneal oil administration can interfere with the outcome of subsequent experiments. As a proof of principle, intraperitoneal peanut oil injection was compared with its oral delivery in a thioglycolate-induced peritonitis model. The chronic peritoneal inflammation due to peanut oil injection impeded the proper recruitment of macrophages and the resolution of inflammation in this peritonitis model. In summary, the data indicate that it is advisable to deliver lipophilic substances, like tamoxifen, by oral gavage instead of intraperitoneal injection. IMPLICATIONS: This work contributes to the reproducibility of animal research by helping to understand some of the undesired effects observed in animal experiments.

Specialized immune responses in the peritoneal cavity and omentum

The peritoneal cavity is a fluid filled space that holds most of the abdominal organs, including the omentum, a visceral adipose tissue that contains milky spots or clusters of leukocytes that are organized similar to those in conventional lymphoid tissues. A unique assortment of leukocytes patrol the peritoneal cavity and migrate in and out of the milky spots, where they encounter Ags or pathogens from the peritoneal fluid and respond accordingly. The principal role of leukocytes in the peritoneal cavity is to preserve tissue homeostasis and secure tissue repair. However, when peritoneal homeostasis is disturbed by inflammation, infection, obesity, or tumor metastasis, specialized fibroblastic stromal cells and mesothelial cells in the omentum regulate the recruitment of peritoneal leukocytes and steer their activation in unique ways. In this review, the types of cells that reside in the peritoneal cavity, the role of the omentum in their maintenance and activation, and how these processes function in response to pathogens and malignancy will be discussed.

The omentum harbors unique conditions in the peritoneal cavity to promote healing and regeneration for diaphragm muscle repair in mdx mice

Although the primary cause of Duchenne muscular dystrophy (DMD) is a genetic mutation, the inflammatory response contributes directly to severity and exacerbation of the diaphragm muscle pathology. The omentum is a lymphoid organ with unique structural and immune functions serving as a sanctuary of hematopoietic and mesenchymal progenitors that coordinate immune responses in the peritoneal cavity. Upon activation, these progenitors expand and the organ produces large amounts of growth factors orchestrating tissue regeneration. The omentum of mdx mouse, a DMD murine model, is rich in milky spots and produces growth factors that promote diaphragm muscle regeneration. The present review summarizes the current knowledge of the omentum as an important immunologic structure and highlights its contribution to resolution of dystrophic muscle injury by providing an adequate environment for muscle regeneration, thus being a potential site for therapeutic interventions in DMD.

LC-QTOF-MS and 1H NMR Metabolomics Verifies Potential Use of Greater Omentum for Klebsiella pneumoniae Biofilm Eradication in Rats

Bacterial wound infections are a common problem associated with surgical interventions. In particular, biofilm-forming bacteria are hard to eradicate, and alternative methods of treatment based on covering wounds with vascularized flaps of tissue are being developed. The greater omentum is a complex organ covering the intestines in the abdomen, which support wound recovery following surgical procedures and exhibit natural antimicrobial activity that could improve biofilm eradication. We investigated changes in rats’ metabolome following Klebsiella pneumoniae infections, as well as the greater omentum’s ability for Klebsiella pneumoniae biofilm eradication. Rats received either sterile implants or implants covered with Klebsiella pneumoniae biofilm (placed in the peritoneum or greater omentum). Metabolic profiles were monitored at days 0, 2, and 5 after surgery using combined proton nuclear magnetic resonance (¹H NMR) and high performance liquid chromatography quadrupole time-of-flight tandem mass spectrometry (LC–QTOF-MS) measurements of urine samples followed by chemometric analysis. Obtained results indicated that grafting of the sterile implant to the greater omentum did not cause major disturbances in rats’ metabolism, whereas the sterile implant located in the peritoneum triggered metabolic perturbations related to tricarboxylic acid (TCA) cycle, as well as choline, tryptophan, and hippurate metabolism. Presence of implants colonized with Klebsiella pneumoniae biofilm resulted in similar levels of metabolic perturbations in both locations. Our findings confirmed that surgical procedures utilizing the greater omentum may have a practical use in wound healing and tissue regeneration in the future.

The Greater Omentum-A Vibrant and Enigmatic Immunologic Organ Involved in Injury and Infection Resolution

Once thought of as an inert fatty tissue present only to provide insulation for the peritoneal cavity, the omentum is currently recognized as a vibrant immunologic organ with a complex structure uniquely suited for defense against pathogens and injury. The omentum is a source of resident inflammatory and stem cells available to participate in the local control of infection, wound healing, and tissue regeneration. It is intimately connected with the systemic vasculature and communicates with the central nervous system and the hypothalamic pituitary adrenal axis. Furthermore, the omentum has the ability to transit the peritoneal cavity and sequester areas of inflammation and injury. It contains functional, immunologic units commonly referred to as "milky spots" that contribute to the organ's immune response. These milky spots are complex nodules consisting of macrophages and interspersed lymphocytes, which are gateways for the infiltration of inflammatory cells into the peritoneal cavity in response to infection and injury. The omentum contains far greater complexity than is currently conceptualized in clinical practice and investigations directed at unlocking its beneficial potential may reveal new mechanisms underlying its vital functions and the secondary impact of omentectomy for the staging and treatment of a variety of diseases.

Human lung organoids develop into adult airway-like structures directed by physico-chemical biomaterial properties

Tissues derived from human pluripotent stem cells (hPSCs) often represent early stages of fetal development, but mature at the molecular and structural level when transplanted into immunocompromised mice. hPSC-derived lung organoids (HLOs) transplantation has been further enhanced with biomaterial scaffolds, where HLOs had improved tissue structure and cellular differentiation. Here, our goal was to define the physico-chemical biomaterial properties that maximally enhanced transplant efficiency, including features such as the polymer type, degradation, and pore interconnectivity of the scaffolds. We found that transplantation of HLOs on microporous scaffolds formed from poly (ethylene glycol) (PEG) hydrogel scaffolds inhibit growth and maturation, and the transplanted HLOs possessed mostly immature lung progenitors. On the other hand, HLOs transplanted on poly (lactide-co-glycolide) (PLG) scaffolds or polycaprolactone (PCL) led to tube-like structures that resembled both the structure and cellular diversity of an adult airway. Our data suggests that scaffold pore interconnectivity and polymer degradation contributed to the maturation, and we found that the size of the airway structures and the total size of the transplanted tissue was influenced by the material degradation rate. Collectively, these biomaterial platforms provide a set of tools to promote maturation of the tissues and to control the size and structure of the organoids.

Considerations for an Alternative Site of Islet Cell Transplantation

Islet cell transplantation has been limited most by poor graft survival. Optimizing the site of transplantation could improve clinical outcomes by minimizing required donor cells, increasing graft integration, and simplifying the transplantation and monitoring process. In this article, we review the history and significant human and animal data for clinically relevant sites, including the liver, spleen, and kidney subcapsule, and identify promising new sites for further research. While the liver was the first studied site and has been used the most in clinical practice, the majority of transplanted islets become necrotic. We review the potential causes for graft death, including the instant blood-mediated inflammatory reaction, exposure to immunosuppressive agents, and low oxygen tension. Significant research exists on alternative sites for islet cell transplantation, suggesting a promising future for patients undergoing pancreatectomy.

The CXCL12-CXCR4/CXCR7 axis as a mechanism of immune resistance in gastrointestinal malignancies

Single agent checkpoint inhibitor therapy has not been effective for most gastrointestinal solid tumors, but combination therapy with drugs targeting additional immunosuppressive pathways is being attempted. One such pathway, the CXCL12-CXCR4/CXCR7 chemokine axis, has attracted attention due to its effects on tumor cell survival and metastasis as well as immune cell migration. CXCL12 is a small protein that functions in normal hematopoietic stem cell homing in addition to repair of damaged tissue. Binding of CXCL12 to CXCR4 leads to activation of G protein signaling kinases such as P13K/mTOR and MEK/ERK while binding to CXCR7 leads to β-arrestin mediated signaling. While some gastric and colorectal carcinoma cells have been shown to make CXCL12, the primary source in pancreatic cancer and peritoneal metastases is cancer-associated fibroblasts. Binding of CXCL12 to CXCR4 and CXCR7 on tumor cells leads to anti-apoptotic signaling through Bcl-2 and survivin upregulation, as well as promotion of the epithelial-to-mesechymal transition through the Rho-ROCK pathway and alterations in cell adhesion molecules. High levels of CXCL12 seen in the bone marrow, liver, and spleen could partially explain why these are popular sites of metastases for many tumors. CXCL12 is a chemoattractant for lymphocytes at lower levels, but becomes chemorepellant at higher levels; it is unclear exactly what gradient exists in the tumor microenvironment and how this influences tumor-infiltrating lymphocytes. AMD3100 (Plerixafor or Mozobil) is a small molecule CXCR4 antagonist and is the most frequently used drug targeting the CXCL12-CXCR4/CXCR7 axis in clinical trials for gastrointestinal solid tumors currently. Other small molecules and monoclonal antibodies against CXCR4 are being trialed. Further understanding of the CXCL12- CXCR4/CXCR7 chemokine axis in the tumor microenvironment will allow more effective targeting of this pathway in combination immunotherapy.

Omentum a powerful biological source in regenerative surgery

The Omentum is a large flat adipose tissue layer nestling on the surface of the intra-peritoneal organs. Besides fat storage, omentum has key biological functions in immune-regulation and tissue regeneration.

Omentum biological properties include neovascularization, haemostasis, tissue healing and regeneration and as an in vivo incubator for cells and tissue cultivation. Some of these properties have long been noted in surgical practice and used empirically in several procedures.

In this review article, the author tries to highlight the omentum biological properties and their application in regenerative surgery procedures. Further, he has started a process of standardisation of basic biological principles to pave the way for future surgical practice.

Antibacterial spectrum of human omentum and differential expression of beta defensins

BACKGROUND

Human β defensins (hBD1 and hBD2) are cationic, cysteine-rich peptides and form an integral part of the mammalian innate immune system. hBD1 is constitutively expressed in epithelial cells, whereas hBD2 increases in response to bacterial infection. Human omentum is known for its anti-inflammatory properties and also possesses an antibacterial activity of its own. We hypothesized that antimicrobial peptides, β defensins, may govern host defense mechanism in the microbe-rich environment of the peritoneal cavity. Therefore, we analyzed the expression of hBD1 and hBD2 in omentum tissue in vivo and also studied the antibacterial activity of omentum against common pathogens.

METHODOLOGY

Omentum tissues were obtained from 30 patients (15 cases and 15 controls). Real-time polymerase chain reaction (PCR) was used to evaluate the mRNA expression of hBD1 and hBD2. Protein quantification was done using Western blotting technique. Antibacterial susceptibility was performed to check the antibacterial activity of omentum.

RESULT

Significantly higher expression of hBD2 was observed in cases compared to controls at both the transcriptional and translational levels. In comparison with an array of antibiotics, activated omentum also showed antibacterial property even at lower concentration of its extract.

CONCLUSION

Omentum directly responds to bacterial infection, which may be due to differential expression of hBD1 and hBD2 in human omental tissue. These peptides (hBD1 and hBD2) may be an ideal candidate for novel antibiotic class with a broad-spectrum activity.

Challenges in Microsurgical Reconstruction for Craniofacial Osteomyelitis With Resultant Osteonecrosis

INTRODUCTION

Chronic osteomyelitis is characterized by compromised blood supply and eventual osteonecrosis. Definitive treatment requires aggressive resection of affected bone. The resultant defect poses a unique challenge to reconstructive surgeons. Much of the literature on craniofacial osteomyelitis focuses on infection eradication, rather than subsequent reconstruction. This article reports representative cases from our experience with free flap reconstruction for defects secondary to chronic osteomyelitis of the craniofacial skeleton.

METHODS/RESULTS

The authors selected 5 of the most difficult reconstructive cases of craniofacial osteomyelitis from our experience in a single tertiary referral institution with a follow-up of at least 6 months. Three of the 5 cases arose in the setting of previous head and neck cancer treated with resection and radiation therapy. One case had a previous surgical craniotomy complicated by osteomyelitis and multiple failed alloplastic reconstructions. The final case was due to multiple gunshots to the head, with subsequent cerebral and cranial abscess (>1000cc). In each case, the defect was successfully treated with free tissue transfer. Two cases required creation of recipient vessels with an arteriovenous loop.

CONCLUSIONS

Free tissue transfer provides a versatile and effective tool in the reconstruction of extensive craniofacial osteomyelitis defects. Furthermore, the addition of vascularized tissue can protect against further episodes of osteomyelitis. Finally, arteriovenous loops can be employed successfully when prior radiation and infection of the wound bed precludes the use of local recipient target vessels.

Therapeutic delivery to the peritoneal lymphatics: Current understanding, potential treatment benefits and future prospects

The interest in approaches to deliver therapeutics to the lymphatic system has increased in recent years as the lymphatics have been discovered to play an important role in a range of disease states such as cancer metastases, inflammatory and metabolic disease, and acute and critical illness. Therapeutic delivery to lymph has the potential to enhance treatment of these conditions. Currently much of the existing data explores therapeutic delivery to the lymphatic vessels and nodes that drain peripheral tissues and the intestine. Relatively little focus has been given to understanding the anatomy, function and therapeutic delivery to the peritoneal lymphatics. Gaining a better understanding of peritoneal lymphatic structure and function would contribute to the understanding of disease processes involving these lymphatics and facilitate the development of delivery systems to target therapeutics to the peritoneal lymphatics. This review explores the basic anatomy and ultrastructure of the peritoneal lymphatics system, the lymphatic drainage pathways from the peritoneum, and therapeutic and delivery system characteristics (size, lipophilicity and surface properties) that favour lymph uptake and retention after intraperitoneal delivery. Finally, techniques that can be used to quantify uptake into peritoneal lymph are outlined, providing a platform for future studies.

Bone tissue engineering in the greater omentum is enhanced by a periosteal transplant in a miniature pig model

Aim: Reconstruction of bone defects with autologous grafts has certain disadvantages. The aim of this study is to introduce a new type of living bioreactor for engineering of bone flaps and to evaluate the effect of different barrier membranes. Materials & methods: Scaffolds loaded with bone morphogenetic proteins and bone marrow aspirate wrapped with either a collagen membrane or a periosteal flap were implanted in the greater omentum of miniature pigs. Results: Both histological and radiographic evaluation showed proven bone formation and increased density after 8 and 16 weeks, with an enhanced effect of the periosteal transplant. Conclusion: The greater omentum is a suitable bioreactor for bone tissue engineering. Endocultivation is both an innovative and promising approach in regenerative medicine.

Effectiveness of bioengineered islet cell sheets for the treatment of diabetes mellitus

BACKGROUND

The present study aimed to evaluate whether bioengineered mouse islet cell sheets can be used for the treatment of diabetes mellitus.

METHODS

Isolated mouse pancreatic islets were dispersed, and cells were plated on temperature-responsive culture plates coated with iMatrix-551. On day 3 of culture, the sheets were detached from the plates and used for further analysis or transplantation. The following parameters were assessed: (1) morphology, (2) expression of β-cell-specific transcription factors and other islet-related proteins, (3) methylation level of the pancreatic duodenal homeobox-1 (Pdx-1) promoter, as determined by bisulfite sequencing, and (4) levels of serum glucose after transplantation of one or two islet cell sheets into the abdominal cavity of streptozotocin-induced diabetic severe combined immunodeficiency mice.

RESULTS

From each mouse, we recovered approximately 233.3 ± 12.5 islets and 1.4 ± 0.1 × 10⁵ cells after dispersion. We estimate that approximately 68.2% of the cells were lost during dispersion. The viability of recovered single cells was 91.3 ± 0.9%. The engineered islet cell sheets were stable, but the messenger RNA levels of various β-cell-specific transcription factors were significantly lower than those of primary islets, whereas Pdx-1 promoter methylation and the expression of NeuroD, Pdx-1, and glucagon proteins were similar between sheets and islets. Moreover, transplantation of islet cell sheets did not revert serum hyperglycemia in any of the recipient mice.

CONCLUSIONS

Engineering effective islet cell sheets require further research efforts, as the currently produced sheets remain functionally inferior compared with primary islets.

Preliminary Evaluation of the Viability of Peritoneal Drainage Catheters Implanted in Rats for Extended Durations

Purpose/Aim: In developing a novel peritoneal oxygenation therapy, catheters implanted into the peritoneal cavity became obstructed with omental tissue and prevented the infusion and removal of fluid from the peritoneal cavity. The obstruction of peritoneal catheters is a significant failure in researching various peritoneal treatments as further fluid administration is no longer possible. The purpose of this preliminary study was to determine the most effective catheter design for infusion and removal of fluid into the peritoneal cavity of rats. Materials and Methods: Four types of catheters were tested including the Jackson-Pratt, round fluted drain, flat fluted drain, and an original design. Three of each catheter type were surgically placed into the peritoneal cavity of rats (n = 12). In order to test the efficacy of each catheter, saline was infused and extracted twice daily. Catheters were scored on a weighted scale based on the amount of time they remained patent, the subjective force needed for extraction/infusion, and the amount of saline removed. Results: The round and flat fluted drain catheters remained patent for the full duration of the study (12 days) compared to the other models which failed after 7 days. These catheters also yielded a high average for extracted saline volume and an easy extraction/infusion. Conclusions: The round and flat fluted drain catheters were recognized as viable options to be used in rats for peritoneal drain studies of up to 12 days.

Selection of Implantation Sites for Transplantation of Encapsulated Pancreatic Islets

Pancreatic islet transplantation has been validated as a valuable therapy for type 1 diabetes mellitus patients with exhausted insulin treatment. However, this therapy remains limited by the shortage of donor and the requirement of lifelong immunosuppression. Islet encapsulation, as an available bioartificial pancreas (BAP), represents a promising approach to enable protecting islet grafts without or with minimal immunosuppression and possibly expanding the donor pool. To develop a clinically implantable BAP, some key aspects need to be taken into account: encapsulation material, capsule design, and implant site. Among them, the implant site exerts an important influence on the engraftment, stability, and biocompatibility of implanted BAP. Currently, an optimal site for encapsulated islet transplantation may include sufficient capacity to host large graft volumes, portal drainage, ease of access using safe and reproducible procedure, adequate blood/oxygen supply, minimal immune/inflammatory reaction, pliable for noninvasive imaging and biopsy, and potential of local microenvironment manipulation or bioengineering. Varying degrees of success have been confirmed with the utilization of liver or extrahepatic sites in an experimental or preclinical setting. However, the ideal implant site remains to be further engineered or selected for the widespread application of encapsulated islet transplantation.

Augmentation of diaphyseal fractures of the radius and ulna in toy breed dogs using a free autogenous omental graft and bone plating

Objectives: Evaluation of the short-term outcome, duration of bone healing, and complications following bone plate fixation in dogs weighing [uni2264]6 kg, with and without the use of a free autogenous greater omental graft (OG).

Materials and methods: A retrospective clinical study reviewed the medical records of 25 dogs of body weight <6 kg with mid to distal diaphyseal fractures of the radius and ulna (29 fractures) treated with open reduction bone plate fixation. Thirteen out of 29 fractures were implanted with an additional 2–3 cm3 OG lateral, cranial, and medial to the fracture site, adjacent to the bone plate.

Results: Median time to radiographic healing in OG fractures (n = 11) was 70 days (range 28–98) compared to 106 days (range: 56–144) in non-OG grafted fractures (n = 14). The OG dogs had no major complications; minor complications included oedema, erythema, and mild osteopenia. Six of the eight non-OG dogs for which follow-up could be obtained developed osteopenia necessitating implant removal, four of which re-fractured the radius one to five months after implant removal, with one dog re-fracturing the limb a second time and resulting in amputation. Telephone follow-up of owners of OG dogs (n = 11) three to 15 months (median 10) post-surgery did not identify any signs of lameness or other complications. Owners of the non-OG dogs (n = 8) reported that there were not any signs of lameness six to 48 months (median 36) post-surgery.

Clinical relevance: Free autogenous omen-tal grafting of diaphyseal fractures of the radius and ulna was associated with radial and ulnar healing with minimal complications in dogs weighing less than 6 kg.

Autogenous hepatic tissue transplantation into the omentum in a novel ectopic liver regeneration murine model

BACKGROUND

Liver regeneration involves hyperplasia and hypertrophy of hepatic cells. The capacity of macroscopic liver tissue to regenerate in ectopic sites is unknown. We aim to develop a novel in vivo model of ectopic liver survivability and regeneration and assess its functionality.

METHODS

Adult male Sprague-Dawley rats (n = 23) were divided into four groups: (1) single-stage (SS) group, wedge liver resection was performed, and the parenchyma was directly implanted into the omentum; (2) double-stage (DS) group, omentum pedicle was transposed over the left hepatic lobe followed by wedge liver resection along with omental flap; (3) Biogel + DS group, rats received intraperitoneal injection of inert polymer particles prior to DS; (4) Biogel + DS + portal vein ligation (PVL) group, Biogel + DS rats underwent subsequent PVL. Hepatobiliary iminodiacetic acid scintigraphy assessed bile excretion from ectopic hepatic implants.

RESULTS

Histologically, the scores of necrosis (P < 0.001) and fibrosis (P = 0.004) were significantly improved in rats undergoing DS procedure (groups 2, 3, and 4) compared with the SS group. Biogel rats (Biogel + DS and Biogel + DS + PVL) demonstrated statistically increased scores of bile duct neoformation (P = 0.002) compared to those without the particles (SS and DS). Scintigraphy demonstrated similar uptake of radiotracer by ectopic hepatic implants in groups 2, 3, and 4.

CONCLUSIONS

Omental transposition provided adequate microcirculation for proliferation of ectopic hepatic cells after liver resection. Inert polymers enhanced the regeneration by promoting differentiation of new bile ducts. The ectopic hepatic implants showed preserved function on scintigraphy. This model provides insights into the capacity of liver parenchyma to regenerate in ectopic sites and the potential as therapeutic target for cell therapy in end-stage liver disease.

The effects of activated omental extract on nuclear and cytoplasmic in vitro maturation of rat oocytes

Objective:

The role of growth factors, including vascular endothelial growth factor of activated omentum on mitosis is clearly known, though not on all the aspects of in vitro oocyte maturation. This study was designed to assess the effect of activated-omental extract (AOE) on in vitro maturation (IVM) of rat cumulus-oocyte complexes (COCs).

Materials and Methods:

In this experimental study, the COCs were incubated in Ham’s F-10 supplemented with either 20% AOE, 20% fetal bovine serum (FBS) or serum-free media. Post-culture COCs were studied according to the cumulus cells (CCs) expansion, nuclear maturation and cytoplasmic maturation. Cumuli expansion was evaluated by inverted microscope without staining; nuclear maturation was assessed by aceto-orcein staining (light microscope) and cytoplasmic maturation was also observed by TEM.

Results:

Expansion of CCs and nuclear maturation of the oocytes in in vitro for 24 hr was significantly higher in AOE- and FBS-supplemented groups (P=0.000 and 0.013) and (P=0.004 and 0.014), respectively, compared to serum-free group. At ultra-structural level, after 24 hr, both FBS and AOE-supplemented media showed uniformly wide perivitelline space (PVS). After 12 hr, the cortical granules were found in the oocytes cultured in FBS and AOE-supplemented media. Within 24 hr, both granules and mitochondria were large without any detectable topographic tendency across the ooplasm. In AOE and FBS-supplemented oocytes, the number and size of microvilli were more than those in serum-free one.

Conclusion:

Although AOE supplementation induced a higher rate of the CCs expansion, and resuming meiosis, it was not as potent as FBS to provide cytoplasmic maturation of rat oocytes.

European Association for Cardio-Thoracic Surgery expert consensus statement on the prevention and management of mediastinitis

Mediastinitis continues to be an important and life-threatening complication after median sternotomy despite advances in prevention and treatment strategies, with an incidence of 0.25-5%. It can also occur as extension of infection from adjacent structures such as the oesophagus, airways and lungs, or as descending necrotizing infection from the head and neck. In addition, there is a chronic form of 'chronic fibrosing mediastinitis' usually caused by granulomatous infections. In this expert consensus, the evidence for strategies for treatment and prevention of mediatinitis is reviewed in detail aiming at reducing the incidence and optimizing the management of this serious condition.