The Fate of the Adipose-Derived Stromal Cells during Angiogenesis and Adipogenesis after Cell-Assisted Lipotransfer:

A novel cryopreservation solution for adipose tissue based on metformin

BACKGROUND

Autologous fat grafting (AFG) often needs multiple sessions due to low volume retention. Young adipose tissue demonstrates a more pronounced therapeutic effect; thus, the cryopreservation of adipose tissue of young origin is particularly crucial. This study investigated the protective effect of a new cryopreservation solution combining trehalose, glycerol, and metformin on adipose tissue.

METHODS

This study initially examined the effect of various concentrations of metformin (0, 1, 2, 4, and 8 mM) on oxidative damage in adipose tissue to identify the optimal concentration. Subsequently, 1.5 mL of fresh human adipose tissue was subjected to freezing using trehalose + glycerol (TG group), trehalose + glycerol + metformin (TGM group), and the common cryoprotectant dimethyl sulfoxide (DMSO) + fetal bovine serum (FBS) (DF group). Samples were cryopreserved in liquid nitrogen for 2 weeks. After thawing, 1 mL of adipose tissue from each group was transplanted subcutaneously into the backs of nude mice. The cryoprotective effects on adipose tissue viability were evaluated during transplantation one month after transplantation.

RESULTS

The 2 mM concentration of metformin exhibited the lowest reactive oxygen species (ROS) level (29.20 ± 1.73) compared to other concentrations (P < 0.05). Cell proliferation and migration assays also supported the superior performance of the 2 mM concentration. Apoptotic analyses of stromal vascular fraction (SVF) cells showed the lowest levels in the 2 mM group. Compared to other cryopreservation groups, the adipose tissue in the TGM group closely resembled fresh adipose tissue in terms of gross structure and histological characteristics, with the lowest apoptosis rate of SVF cells. In vivo analysis revealed the highest tissue retention rate in the TGM group, with histological examination indicating robust structural integrity.

CONCLUSION

The TGM cryopreservation solution, containing metformin, greatly preserves adipose tissue, reduces apoptosis, and improves tissue retention rates. This solution was non-toxic and safe, making it well-suited for tissue cryopreservation in clinical settings.

Aspirin Inhibits the In Vitro Adipogenic Differentiation of Human Adipose Tissue-Derived Stem Cells in a Dose-Dependent Manner

Aspirin (ASA) is one of the most used medications worldwide and has shown various effects on cellular processes, including stem cell differentiation. However, the effect of ASA on adipogenesis of adipose tissue-derived stem cells (ASCs) remains largely unknown. Considering the potential application of ASCs in regenerative medicine and cell-based therapies, this study investigates the effects of ASA on adipogenic differentiation in human ASCs. ASCs were exposed to varying concentrations of ASA (0 µM, 400 µM, and 1000 µM) and evaluated for changes in morphology, migration, and adipogenic differentiation. While ASA exposure did not affect self-renewal potential, migration ability, or cell morphology, it significantly reduced lipid vacuole formation at 1000 µM after 21 days of adipogenic differentiation (p = 0.0025). This visible inhibition correlated with decreased expression of adipogenic markers (PPARG, ADIPOQ, and FABP4) and the proliferation marker MKi67 under ASA exposure in comparison to the control (ns). Overall, the findings demonstrate that ASA inhibits adipogenic differentiation of human ASCs in a dose-dependent manner in vitro, contrasting its known role in promoting osteogenic differentiation. This research highlights ASA's complex effects on ASCs and emphasizes the need for further investigation into its mechanisms and potential therapeutic applications in obesity and metabolic diseases. The inhibitory effects of ASA on adipogenesis should be considered in cell-based therapies using ASCs.

Biomechanics of Negative-Pressure-Assisted Liposuction and Their Influence on Fat Regeneration

Autologous fat grafting has been widely adopted in cosmetic and reconstructive procedures recently. With the emerging of negative-pressure-assisted liposuction system, the harvesting process of fat grafting is more standardized, controllable, and efficient. Each component in the system could influence the biomechanical environment of lipoaspirate. Several reviews have studied the impact of negative pressure on fat regeneration. As the initial part of the harvesting system, cannulas possess their unique mechanical parameters and their influence on lipoaspirate biomechanical characters, biological behaviors, and regeneration patterns remains unclear. Basic in vivo and in vitro studies have been performed to determine the possible mechanisms. Instant in vivo studies focus on adipocytes, stromal vascular fraction cells, fat particles, and growth factors, while in vivo grafting experiments analyze the graft retention rate and histology. Understanding the different regeneration patterns of lipoaspirate and the mechanisms behind may facilitate the choice of harvesting cannulas in clinical practice.

Efficacy and Safety of Cell-Assisted Acellular Adipose Matrix Transfer for Volume Retention and Regeneration Compared to Hyaluronic Acid Filler Injection

BACKGROUND

Cell-assisted acellular adipose matrix (AAM) transfer is a novel technique for soft tissue volume restoration, where AAM acts as a scaffold for tissue proliferation and promotes host cell migration, vascularization, and adipogenesis. This study aimed to evaluate the efficacy and safety of in vivo cell-assisted AAM transfer compared to hyaluronic acid (HA) filler injection.

METHODS

Human adipose tissue was used to manufacture AAM, and murine adipose-derived stem cells (ASCs) were prepared. Nude mice were divided into four groups: AAM transfer (AT), ASC-assisted AAM transfer (CAT), HA filler injection (HI), and ASC-assisted HA filler injection (CHI). Eight weeks post-transfer, in vivo graft volume/weight, histology, and gene expression were analyzed to assess efficacy and safety.

RESULTS

The AAM retained its three-dimensional scaffold structure without cellular components. AT/CAT showed lower volume retention than HA/CHA; however, CAT maintained a similar volume to HA. Histologically, adipogenesis and collagen formation were increased in AT/CAT compared to HA/CHA, with CAT showing the highest levels. CAT also demonstrated superior angiogenesis, adipogenesis, and gene expression (Vegf and Pparg), along with lower Il-6 expression, higher Il-10 expression, and reduced capsule formation, indicating better biocompatibility.

CONCLUSIONS

Cell-assisted AAM transfer is a promising technique for volume retention and tissue regeneration, offering a safe and effective alternative to HA filler injections.

LEVEL OF EVIDENCE III

This journal requires that authors assign a level of evidence to each article. For a full description of these Evidence-Based Medicine ratings, please refer to the Table of Contents or the online Instructions to Authors www.springer.com/00266 .

Survival Mechanisms and Retention Strategies in Large-Volume Fat Grafting: A Comprehensive Review and Future Perspectives

INTRODUCTION

Large-volume fat grafting is emerging as a promising technique in plastic and reconstructive surgery. However, the unpredictable graft volume retention rate remains a critical challenge. To address this issue, we need a profound understanding of the survival mechanisms following large-volume fat transplantation. This review summarizes known survival mechanisms and strategies to enhance graft retention.

METHODS

This review comprehensively examines the current literature on the survival mechanisms and retention strategies in large-volume fat grafting. A thorough literature search was conducted using PubMed, Medline and Google Scholar databases, focusing on studies published from 2009 to 2023.

CONCLUSION

In the current research on fat survival mechanisms, few have focused on large-volume fat grafting. This review provides an overview of the survival mechanisms specific to large-volume fat grafting and identifies a survival pattern distinct from that of small-volume fat grafting. Additionally, we have summarized existing strategies to improve graft retention across five stages (harvesting, processing, enrichment, grafting and post-graft care), analyzed their advantages and disadvantages and identified some of the most promising strategies.

LEVEL OF EVIDENCE IV

This journal requires that authors assign a level of evidence to each article. For a full description of these Evidence-Based Medicine ratings, please refer to the Table of Contents or the online Instructions to Authors   www.springer.com/00266.

Enhancing Fat Transplantation Efficiency in a Mouse Model through Pretreatment of Adipose-Derived Stem Cells with RIP3 Inhibitors

BACKGROUND

Autologous fat transplantation, widely used in cosmetic and reparative surgery for volumetric enhancements, faces challenges with its inconsistent long-term survival rates. The technique's efficacy, crucial for its development, is hindered by unpredictable outcomes. Enriching fat grafts with adipose-derived stem cells (ADSCs) shows promise in improving survival efficiency.

OBJECTIVES

This study aimed to explore the potential of receptor-interacting protein kinase 3 (RIP3) kinase inhibitors as a pretreatment for ADSCs in enhancing autologous fat graft retention over a long term.

METHODS

ADSCs were isolated, cultured under normal or oxygen-glucose deprivation conditions, and mixed with particulate fat grafts to form distinct experimental groups in female nude mice. Fat graft mass and volume, along with underlying mechanisms, were evaluated using quantitative reverse transcription polymerase chain reaction (RT-qPCR), immunohistochemistry, and Western blot analysis.

RESULTS

The experimental group, pretreated with RIP3 kinase inhibitors, had higher graft mass and volume, greater adipocyte integrity, and increased peroxisome proliferator-activated receptor gamma (PPARγ) mRNA levels than control groups. Furthermore, the experimental group demonstrated lower expression of necroptosis pathway proteins in the short term and an ameliorated inflammatory response as indicated by interleukin-1 beta (IL-1β), interleukin-10 (IL-10) mRNA levels, and histological analyses. Notably, enhanced neovascularization was evident in the experimental group.

CONCLUSIONS

These findings suggest that RIP3 kinase inhibitor pretreatment of ADSCs can improve fat graft survival, promote adipocyte integrity, potentially decrease inflammation, and enhance neovascularization.

NO LEVEL ASSIGNED

This journal requires that authors assign a level of evidence to each submission to which Evidence-Based Medicine rankings are applicable. This excludes Review Articles, Book Reviews, and manuscripts that concern Basic Science, Animal Studies, Cadaver Studies, and Experimental Studies. For a full description of these Evidence-Based Medicine ratings, please refer to the Table of Contents or the online Instructions to Authors www.springer.com/00266 .

Effects of Nanofat in Plastic and Reconstructive Surgery: A Systematic Review

BACKGROUND

Since nanofat was first introduced by Tonnard in 2013, numerous studies have reported positive findings with its use; however, concerns exist regarding its effects and mechanisms, and the various methods used to generate nanofat also remain unclear. The authors conducted a systematic review to evaluate the efficacy of nanofat grafting alone in plastic and reconstructive surgery.

METHODS

The MEDLINE, Embase, Cochrane Central, Web of Science, and Scopus databases were searched for studies related to the use of nanofat grafting alone in plastic and reconstructive surgery. Outcomes of interest were all clinical results in humans or animals.

RESULTS

Twelve studies were included. No meta-analysis was conducted due to the clinical heterogeneity of the studies. In general, included studies had a low level of evidence. Six studies ( n = 253 patients) showed significant improvements in scar characteristics based on Patient and Observer Scar Assessment Scale, FACE-Q scale, physician assessment, patient satisfaction, and Vancouver Scar Scale scores. Four studies described the benefits of nanofat in skin rejuvenation (wrinkles, fine rhytides, pigmentation, and discoloration) through photographs, questionnaires, and indentation indices. Histologic evaluation illustrated overall increases in skin thickness, collagen, and elastic fibers. Three experimental studies showed the beneficial effects of nanofat on fat grafting, diabetic wound healing, and hair growth, with compelling histological evidence. No severe complication was reported.

CONCLUSIONS

Nanofat grafting shows potential benefits in scar and antiaging treatments, with conclusive histological evidence. Clinical studies of fat grafting, wound healing, and hair growth should be conducted, based on the results of this systematic review. Nanofat grafting could be a practical and safe procedure.

Evaluating the Efficacy of Dedifferentiated Fat Cells (DFATs) vs Adipose-Derived Stem Cells (ASCs) in Enhancing the Viability of Fat Grafts

BACKGROUND

Enhancing graft fat survival remains a paramount challenge in autologous fat transplantation surgeries. Dedifferentiated fat cells (DFATs) and adipose-derived stem cells (ASCs) represent 2 pivotal cells with potential to improve fat graft survival rates.

OBJECTIVES

In this study we aimed to compare the effectiveness of DFATs and ASCs in promoting fat graft survival, emphasizing their adipogenic and angiogenic capabilities.

METHODS

Both in vitro and in vivo experiments were conducted. In vitro assessments compared adipogenesis, angiogenesis, osteogenesis, chondrogenesis, cell migration abilities, and surface markers. For in vivo evaluation, a cell-assisted lipotransfer animal model was employed to gauge graft volume retention and histological morphology. Analysis techniques included hematoxylin and eosin staining, Western blotting, and real-time polymerase chain reaction.

RESULTS

In vitro findings suggested a slight superiority of DFATs in adipogenesis and angiogenesis compared to ASCs. In vivo tests demonstrated both cell types surpassed the control in terms of graft volume retention, with the DFATs group marginally outperforming in retention rates and the ASC group presenting a slightly enhanced graft tissue structure.

CONCLUSIONS

Our study underscores the distinct advantages of DFATs and ASCs in bolstering fat graft survival, offering potentially novel insights for plastic surgeons aiming to elevate fat graft survival rates.

Histological Comparison of Nanofat and Lipoconcentrate: Enhanced Effects of Lipoconcentrate on Adipogenesis and Angiogenesis

BACKGROUND

Nanofat and lipoconcentrate contain adipose-derived stem cells and growth factors, and have wide clinical applications in the regenerative field. This study aimed to investigate the microenvironmental changes associated with nanofat and lipoconcentrate.

METHODS

Conventional fat, nanofat, or lipoconcentrate (0.2 mL each, n = 5 per group) were injected subcutaneously into the dorsal flanks of athymic nude mice. The graft weights were measured at postoperative week 4; the grafts and their overlying skin were used for histological analyses.

RESULTS

Weights of the lipoconcentrate grafts were significantly greater than those of the conventional fat (p < 0.05) and nanofat (p < 0.01) grafts. There was no significant difference in inflammation, oil cysts, and fibrosis between the conventional fat and nanofat groups. Histological examination of the lipoconcentrate grafts showed less macrophage infiltration and the formation of fibrosis and oil cysts. Additionally, adipogenesis and angiogenesis were induced more in the lipoconcentrate grafts than in the nanofat grafts (p < 0.01). Lipoconcentrate and nanofat improved dermal thickness (p < 0.001 and p < 0.01, respectively, versus the baseline).

CONCLUSION

Lipoconcentrate grafts had greater volume and shape retention than conventional fat and nanofat grafts. They had better histological structure and acted as scaffolds for adipogenesis and angiogenesis. Both products showed regenerative effects on dermal thickness; however, only lipoconcentrate grafts had the required volume and regenerative effects, allowing it to serve as a novel adipose-free grafting method for facial rejuvenation and contouring.

NO LEVEL ASSIGNED

This journal requires that authors assign a level of evidence to each submission to which Evidence-Based Medicine rankings are applicable. This excludes Review Articles, Book Reviews, and manuscripts that concern Basic Science, Animal Studies, Cadaver Studies, and Experimental Studies. For a full description of these Evidence-Based Medicine ratings, please refer to Table of Contents or the online Instructions to Authors www.springer.com/00266 .

Enhanced Effect of Secondary Administration of Adipose-Derived Stromal Cells Concurrent with Fat Grafting

BACKGROUND

Cell-assisted lipotransfer, a fat graft mixed with adipose-derived stromal cells, is known to enhance fat graft retention. Previously, the authors showed that intravenous injection of adipose-derived stromal cells can improve the survival of grafted fat. In the present study, the authors investigated the effects of a secondary intravenous injection of adipose-derived stromal cells on fat grafting.

METHODS

Wild-type C57BL/6J (B6) mice were used as donors for grafted fat and as recipients. Adipose-derived stromal cells were harvested from green fluorescent protein and DsRed B6 mice. The recipient mice were divided into three groups: SI ( n = 10), RI1 ( n = 10), and RI2 ( n = 11). All groups received intravenous injections of green fluorescent protein adipose-derived stromal cells immediately after fat grafting. The RI1 and RI2 groups received repeated intravenous injections of DsRed adipose-derived stromal cells at 1 and 2 weeks, respectively, after fat grafting. The grafted fat volume was measured using micro-computed tomography.

RESULTS

Secondarily injected DsRed adipose-derived stromal cells were recruited to the grafted fat and resulted in a higher retention of graft volume and vascular density ( P < 0.05). The stromal-derived factor-1 and C-X-C chemokine receptor type 4 genes related to stem cell homing were highly expressed in the grafted fat and adipose-derived stromal cells ( P < 0.05). The RI2 group showed a higher graft volume and vascular density than the SI and RI1 groups ( P < 0.05).

CONCLUSIONS

A secondary intravenous injection of adipose-derived stromal cells at a 2-week interval enhances the effect of adipose-derived stromal cell enrichment in fat grafting. These findings refine clinical protocols and enhance the therapeutic value of cell-assisted lipotransfer.

CLINICAL RELEVANCE STATEMENT

In a modified animal model of cell-assisted lipotransfer, the authors demonstrated that secondary intravenous administration of adipose-derived stromal cells improved retention of grafted fat.

The Evolving Function of Vasculature and Pro-angiogenic Therapy in Fat Grafting

Autologous fat grating is a widely-accepted method to correct soft tissue deficiency. Although fat transplantation shows excellent biocompatibility and simple applicability, the relatively low retention rate caused by fat necrosis is still a challenge. The vasculature is integral after fat grafting, serving multiple crucial functions. Rapid and effective angiogenesis within grafts is essential for supplying oxygen necessary for adipocytes' survival. It facilitates the influx of inflammatory cells to remove necrotic adipocytes and aids in the delivery of regenerative cells for adipose tissue regeneration in fat grafts. The vasculature also provides a niche for interaction between adipose progenitor cells and vascular progenitor cells, enhancing angiogenesis and adipogenesis in grafts. Various methods, such as enriching grafts with diverse pro-angiogenic cells or utilizing cell-free approaches, have been employed to enhance angiogenesis. Beige and dedifferentiated adipocytes in grafts could increase vessel density. This review aims to outline the function of vasculature in fat grafting and discuss different cell or cell-free approaches that can enhance angiogenesis following fat grafting.

Extracellular Vesicles Derived From Hypoxia-Treated Human Adipose Stem Cells Increase Proliferation and Angiogenic Differentiation in Human Adipose Stem Cells

BACKGROUND

Adipose-derived stem cells (ADSCs) are crucial in cell-assisted lipotransfer (CAL). ADSC-derived exosomes could improve the survival of CAL. Almost all relevant research now ignores ADSCs in favor of studying the proangiogenic potential of extracellular vesicles (EVs) on human umbilical vein endothelial cells (HUVECs).

OBJECTIVES

Given the significance of ADSCs in CAL, the authors sought to verify that EVs from ADSCs under hypoxia treatment can enhance the angiogenic potential of ADSCs.

METHODS

EVs were harvested from human ADSCs (hADSCs) under normoxia and hypoxia. A Cell Counting Kit-8 (CCK-8) assay was used to measure the proliferation of hADSCs. By examining the expression of CD31, vascular endothelial growth factor receptor 2, and vascular endothelial growth factor, the pro-angiogenic differentiation potential was assessed. Moreover, a tube formation experiment was carried out to evaluate the pro-angiogenic differentiation potential.

RESULTS

Hypoxic EVs showed more significant pro-proliferative and pro-angiogenic potential. Angiogenesis was more vigorous in hADSCs treated with hypoxic EVs than in those treated with nomorxic EVs. The hADSCs treated with hypoxic EVs expressed higher angiogenic markers, according to real-time polymerase chain reaction (RT-PCR) and Western blot analysis, which revealed more angiogenic marker expression in hypoxic EV-treated hADSCs. The same result was demonstrated by tube formation on Matrigel in vitro.

CONCLUSIONS

Hypoxic EVs significantly increased the proliferation and angiogenic differentiation potential of hADSCs. Hypoxic EV-treated ADSCs may be beneficial to CAL and prevascularized tissue-engineered constructs.

Fat Graft Survival Requires Metabolic Reprogramming Toward the Glycolytic Pathway

BACKGROUND

Fat grafts are widely used as natural fillers in reconstructive and cosmetic surgery. However, the mechanisms underlying fat graft survival are poorly understood. Here, we performed an unbiased transcriptomic analysis in a mouse fat graft model to determine the molecular mechanism underlying free fat graft survival.

METHODS

We conducted RNA-sequencing (RNA-seq) analysis in a mouse free subcutaneous fat graft model on days 3 and 7 following grafting (n = 5). High-throughput sequencing was performed on paired-end reads using NovaSeq6000. The calculated transcripts per million (TPM) values were processed for principal component analysis (PCA), unsupervised hierarchically clustered heat map generation, and gene set enrichment analysis.

RESULTS

PCA and heat map data revealed global differences in the transcriptomes of the fat graft model and the non-grafted control. The top meaningful upregulated gene sets in the fat graft model were related to the epithelial-mesenchymal transition and hypoxia on day 3, and angiogenesis on day 7. Mechanistically, the glycolytic pathway was upregulated in the fat graft model at days 3 (FDR q = 0.012) and 7 (FDR q = 0.084). In subsequent experiments, pharmacological inhibition of the glycolytic pathway in mouse fat grafts with 2-deoxy-D-glucose (2-DG) significantly suppressed fat graft retention rates, both grossly and microscopically (n = 5).

CONCLUSIONS

Free adipose tissue grafts undergo metabolic reprogramming toward the glycolytic pathway. Future studies should examine whether targeting this pathway can enhance the graft survival rate.

DATA AND MATERIALS AVAILABILITY

RNA-seq data were deposited in the Gene Expression Omnibus (GEO) database under accession number GSE203599.

Strategies to Improve AFT Volume Retention After Fat Grafting

BACKGROUND

Autologous fat grafting has gained increasing popularity used in plastic surgery as a strategy to improve functional and aesthetic outcome. However, variable augmentation results have concerned surgeons in that volume loss of grafted fat reported fluctuates unsteadily.

AIM

An optimal technique that clinically maximizes the long-term survival rate of transplantation is in urgent need to be identified.

METHOD

The PubMed/MEDLINE database was queried to search for animal and human studies published through March of 2022 with search terms related to adipose grafting encompassing liposuction, adipose graft viability, processing technique, adipose-derived stem cell, SVF and others.

RESULTS

45 in vivo studies met inclusion criteria. The principal of ideal processing technique is effective purification of fat and protection of tissue viability, such as gauze rolling and washing-filtration devices. Cell-assisted lipotransfer including SVF, SVF-gel and ADSCs significantly promotes graft retention via differentiation potential and paracrine manner. ADSCs induce polarization of macrophages to regulate inflammatory response, mediate extracellular matrix remodeling and promote endothelial cell migration and sprouting, and differentiate into adipocytes to replace necrotic cells, providing powerful evidence for the benefits and efficacy of cell-assisted lipotransfer.

CONCLUSION

Based on the current evidence, the best strategy can not be decided. Cell-assisted lipotransfer has great potential for use in regenerative medicine. But so far mechanically prepared SVF-gel is conducive to clinical promotion. PRP as endogenous growth factor sustained-release material shows great feasibility.

LEVEL OF EVIDENCE IV

This journal requires that authors assign a level of evidence to each article. For a full description of these Evidence-Based Medicine ratings, please refer to the Table of Contents or the online Instructions to Authors www.springer.com/00266 .

Combination of PDGF-BB and adipose-derived stem cells accelerated wound healing through modulating PTEN/AKT pathway

Adipose-derived stem cells (ADSCs) have been widely proven to facilitate wound healing. Our study aimed to estimate the influence of combined ADSCs and platelet-derived growth factor-BB (PDGF-BB) on wound healing. We utilized 4 healthy SD rats to isolate ADSCs. Platelet-rich plasma (PRP) was acquired utilizing a two-step centrifugation technology. The role of PRP, PDGF-BB, and PDGF-BB combined with a PI3k inhibitor LY294002 on the viability, migration, and PTEN/AKT pathway in ADSCs were examined utilizing CCK-8, Transwell, and western blot assays. Then, we constructed an open trauma model in SD rats. Effects of ADSCs treated with PDGF-BB on pathological changes, CD31, and PTEN/AKT pathway of wound closure were assessed by hematoxylin & eosin (H&E) staining, Masson staining, immunohistochemical, and western blot assays, respectively. PRP and PDGF-BB intensified the viability and migration of ADSCs by modulating the PTEN/AKT pathway. Interestingly, LY294002 reversed the role of PDGF-BB on ADSCs. In vivo experiments, combined intervention with ADSCs plus PDGF-BB/PRP facilitated wound closure and ameliorated histological injury. Moreover, combined intervention with ADSCs and PDGF-BB attenuated the PTEN level and elevated the CD31 level as well as the ratio of p-AKT/AKT in the skin tissues. A combination of ADSCs and PDGF-BB facilitated wound healing might associate with the regulation of the PTEN/AKT pathway.

Implantation and tracing of green fluorescent protein-expressing adipose-derived stem cells in peri-implant capsular fibrosis

BACKGROUND

Adipose-derived stem cells (ASCs) have been reported to reduce fibrosis in various tissues. In this study, we investigated the inhibitory role of ASCs on capsule formation by analyzing the histologic, cellular, and molecular changes in a mouse model of peri-implant fibrosis. We also investigated the fate and distribution of ASCs in the peri-implant capsule.

METHODS

To establish a peri-implant fibrosis model, customized silicone implants were inserted into the dorsal site of C57BL/6 wild-type mice. ASCs were harvested from the fat tissues of transgenic mice that express a green fluorescent protein (GFP-ASCs) and then injected into the peri-implant space of recipient mice. The peri-implant tissues were harvested from postoperative week 2 to 8. We measured the capsule thickness, distribution, and differentiation of GFP-ASCs, as well as the cellular and molecular changes in capsular tissue following ASC treatment.

RESULTS

Injected GFP-ASCs were distributed within the peri-implant capsule and proliferated. Administration of ASCs reduced the capsule thickness, decreased the number of myofibroblasts and macrophages in the capsule, and decreased the mRNA level of fibrogenic genes within the peri-implant tissue. Angiogenesis was enhanced due to trans-differentiation of ASCs into vascular endothelial cells, and tissue hypoxia was relieved upon ASC treatment.

CONCLUSIONS

We uncovered that implanted ASCs inhibit capsule formation around the implant by characterizing a series of biological alterations upon ASC treatment and the fate of injected ASCs. These findings highlight the value of ASCs for future clinical applications in the prevention of capsular contracture after implant-based reconstruction surgery.

Oncologic Safety and Efficacy of Cell-Assisted Lipotransfer for Breast Reconstruction in a Murine Model of Residual Breast Cancer

BACKGROUND

Cell-assisted lipotransfer (CAL) is a novel technique for fat grafting that combines the grafting of autologous fat and adipose-derived stromal cells (ASCs) to enhance fat graft retention; however, its oncologic safety is controversial.

METHODS

Herein, we investigated the oncologic safety of CAL for breast reconstruction using a murine model of residual breast cancer. Various concentrations of 4T1 cells (murine breast cancer cells) were injected into female mastectomized BALB/c mice to determine the appropriate concentration for injection. One week after injection, mice were divided into control (100 μL fat), low CAL (2.5 × 10⁵ ASCs/100 μL fat), and high CAL (1.0 × 10⁶ ASCs/100 μL fat) groups, and fat grafting was performed. The injection of 5.0 × 10³ 4T1 cells was appropriate to produce a murine model of residual breast cancer.

RESULTS

The weight of the fat tumor mass was significantly higher in the high CAL group than in the other groups (p < 0.05). However, the estimated tumor weight was not significantly different between the groups. Additionally, the fat graft survival rate was significantly higher in the high CAL group than in the control and low CAL groups (p < 0.05). No significant difference was noted in the percentage of Ki-67-positive cells, suggesting that tumor proliferation was not significantly different between the groups.

CONCLUSION

In summary, CAL significantly improved fat graft survival without affecting tumor size and proliferation in a murine model of residual breast cancer. These results highlight the oncologic safety of CAL for breast reconstruction.

NO LEVEL ASSIGNED

This journal requires that authors assign a level of evidence to each submission to which Evidence-Based Medicine rankings are applicable. This excludes Review Articles, Book Reviews, and manuscripts that concern Basic Science, Animal Studies, Cadaver Studies, and Experimental Studies. For a full description of these Evidence-Based Medicine ratings, please refer to the Table of Contents or the online Instructions to Authors www.springer.com/00266 .

A Bibliometric and Visualization Analysis on the Research of Fat Grafting from 1945 to 2021

BACKGROUND

It is very important to generate a comprehensive assessment of the fat grafting field due to the rapid growth of scientific literature. The current study aimed to use bibliometric analysis to evaluate fat grafting research qualitatively and quantitatively and determine the research hotspots and trends in this field.

METHODS

Publications on fat grafting research were extracted from the Web of Science core collection database. VOSviewer 1.6.18 was applied to perform the bibliometric analysis of these articles.

RESULTS

A total of 2558 studies published by 594 different journals authored by 9097 researchers were contained in this study. In the co-authorship analysis, the bulk of the retrieved studies was conducted by the USA, followed by China, Italy and Japan, while the most productive institution, journal and author were Chinese Academy of Medicine Sciences, Plastic and Reconstruction Surgery and Klinger M, respectively. In the co-cited analysis, the most top cited author, journal, organization and country were Coleman Sr, Plastic and Reconstruction Surgery, New York University and the USA, respectively. The map of keywords occurrence revealed the most active research aspects were focused on "surgery," "cell," "breast reconstruction" and "survival" and the time overlay mapping showed that the most active research hotspots were "breast reconstruction" and "retention".

CONCLUSIONS

The research hotspots include the following four aspects: aesthetic surgeries, cell-assisted lipotransfer, breast reconstruction and grafted fat survival. Breast fat grafting and volume retention may be trends in the future. We are willing to provide more beneficial data to contribute valuable research for the fat grafting through this study.

LEVEL OF EVIDENCE III

This journal requires that authors assign a level of evidence to each article. For a full description of these Evidence-Based Medicine ratings, please refer to the Table of Contents or the online Instructions to Authors www.springer.com/00266 .

Adipose-derived stem cells exosome and its potential applications in autologous fat grafting

Recently, there has been renewed interest in autologous fat grafting both for its filler and regenerative traits. The universal application, however, has been impeded by the unstable survival rates and complications. There has been substantial research undertaken on the role of adipose-derived stem cells (ADSCs) involved in fat graft fates including angiogenesis, adipogenesis, and inflammatory regulation. As the effectors of their parental cells, ADSC-derived exosomes (ADSC-exos) encapsulating multiple bioactive cargoes mediate cell-to-cell communication in a paracrine manner. ADSC-exos have received much attention for their biocompatible and efficient therapeutic potentials as "cell-free therapy" in plastic surgery, including increasing fat grafting survival rates. In this review, we summarize the current knowledge about the biological basis of ADSC-exos, ADSC-related mechanisms of fat survival, research updates of ADSC-exos in autologous fat grafting, and discuss some challenges along with research prospects.

Dedifferentiation of Human Adipocytes After Fat Transplantation

BACKGROUND

Fat transplantation is a common method employed to treat soft-tissue defects. The dedifferentiation of mature adipocytes has been well documented, but whether it occurs after fat transplantation remains unclear.

OBJECTIVES

The major purpose of this project was to investigate the dedifferentiation of mature adipocytes after fat transplantation.

METHODS

Human lipoaspirate tissue was obtained from 6 female patients who underwent esthetic liposuction. Mature adipocytes were extracted and labeled with PKH26, mixed with lipoaspirate, and injected into nude mice. In addition, PKH26+ adipocytes were subjected to a ceiling culture. Grafted fat was harvested from nude mice, and stromal vascular fragment cells were isolated. The immunophenotype of PKH26+ cells was detected by flow cytometry analysis at 2 days and 1 week. The PKH26+ cells were sorted and counted at 2 and 4 weeks to verify their proliferation and multilineage differentiation abilities.

RESULTS

Two days after transplantation, almost no PKH26+ cells were found in the stromal vascular fragment cells. The PKH26+ cells found 1 week after transplantation showed a positive expression of cluster of differentiation (CD) 90 (CD90) and CD105 and a negative expression of CD45. This indicates that the labeled adipocytes were dedifferentiated. Its pluripotency was further demonstrated by fluorescent cell sorting and differentiation culture in vitro. In addition, the number of live PKH26+ cells at week 4 [(6.83 ± 1.67) × 104] was similar with that at week 2 [(7.11 ± 1.82) × 104].

CONCLUSIONS

Human mature adipocytes can dedifferentiate into stem cell-like cells in vivo after fat transplantation.

Spontaneous Browning of White Adipose Tissue Improves Angiogenesis and Reduces Macrophage Infiltration After Fat Grafting in Mice

Background: Fat grafting is a frequently used technique; however, its survival/ regeneration mechanism is not fully understood. The browning of white adipocytes, a process initiated in response to external stimuli, is the conversion of white to beige adipocytes. The physiologic significance of the browning of adipocytes following transplantation is unclear.

Methods: C57BL/6 mice received 150 mg grafts of inguinal adipose tissue, and then the transplanted fat was harvested and analyzed at different time points to assess the browning process. To verify the role of browning of adipocytes in fat grafting, the recipient mice were allocated to three groups, which were administered CL316243 or SR59230A to stimulate or suppress browning, respectively, or a control group after transplantation.

Results: Browning of the grafts was present in the center of each as early as 7 days post-transplantation. The number of beige cells peaked at day 14 and then decreased gradually until they were almost absent at day 90. The activation of browning resulted in superior angiogenesis, higher expression of the pro-angiogenic molecules vascular endothelial growth factor A (VEGF-A) and fibroblast growth factor 21 (FGF21), fewer macrophages, and ultimately better graft survival (Upregulation, 59.17% ± 6.64% vs. Control, 40.33% ± 4.03%, *p < 0.05), whereas the inhibition of browning led to poor angiogenesis, lower expression of VEGF-A, increased inflammatory macrophages, and poor transplant retention at week 10 (Downregulation, 20.67% ± 3.69% vs. Control, 40.33% ± 4.03%, *p < 0.05).

Conclusion: The browning of WAT following transplantation improves the survival of fat grafts by the promotion of angiogenesis and reducing macrophage.

LRG-1 promotes fat graft survival through the RAB31-mediated inhibition of hypoxia-induced apoptosis

Autologous adipose tissue is an ideal soft tissue filling material, and its biocompatibility is better than that of artificial tissue substitutes, foreign bodies and heterogeneous materials. Although autologous fat transplantation has many advantages, the low retention rate of adipose tissue limits its clinical application. Here, we identified a secretory glycoprotein, leucine‐rich‐alpha‐2‐glycoprotein 1 (LRG‐1), that could promote fat graft survival through RAB31‐mediated inhibition of hypoxia‐induced apoptosis. We showed that LRG‐1 injection significantly increased the maintenance of fat volume and weight compared with the control. In addition, higher fat integrity, more viable adipocytes and fewer apoptotic cells were observed in the LRG‐1‐treated groups. Furthermore, we discovered that LRG‐1 could reduce the ADSC apoptosis induced by hypoxic conditions. The mechanism underlying the LRG‐1‐mediated suppression of the ADSC apoptosis induced by hypoxia was mediated by the upregulation of RAB31 expression. Using LRG‐1 for fat grafts may prove to be clinically successful for increasing the retention rate of transplanted fat.

Recent Developments in Extracellular Matrix Remodeling for Fat Grafting

Remodeling of the extracellular matrix (ECM), which provides structural and biochemical support for surrounding cells, is vital for adipose tissue regeneration after autologous fat grafting. Rapid and high-quality ECM remodeling can improve the retention rate after fat grafting by promoting neovascularization, regulating stem cells differentiation, and suppressing chronic inflammation. The degradation and deposition of ECM are regulated by various factors, including hypoxia, blood supply, inflammation, and stem cells. By contrast, ECM remodeling alters these regulatory factors, resulting in a dynamic relationship between them. Although researchers have attempted to identify the cellular sources of factors associated with tissue regeneration and regulation of the microenvironment, the factors and mechanisms that affect adipose tissue ECM remodeling remain incompletely understood. This review describes the process of adipose ECM remodeling after grafting and summarizes the factors that affect ECM reconstruction. Also, this review provides an overview of the clinical methods to avoid poor ECM remodeling. These findings may provide new ideas for improving the retention of adipose tissue after fat transplantation.

Effects of non-vascularized adipose tissue transplantation on its genetic profile

Subcutaneous adipose tissue (SAT) is recognized as a highly active metabolic and inflammatory tissue. Interestingly, adipose tissue transplantation is widely performed in plastic surgery via lipofilling, yet little is known about the gene alteration of adipocytes after transplantation. We performed an RNA-expression analysis of fat transplants before and after fat transplantation.In C57BL/6 N mice SAT was autologously transplanted. Samples of SAT were analysed before transplantation, 7, and 15 days after transplantation and gene expression profiles were measured.Analysis revealed that lipid metabolism-related genes were downregulated while inflammatory and extracellular matrix related genes were up-regulated 7 and 15 days after transplantation. When comparing gene expression profile 7 days after transplantation to 15 days after transplantation developmental pathways showed most changes.

The Effect of Different Diameters of Fat Converters on Adipose Tissue and Its Cellular Components: Selection for Preparation of Nanofat

BACKGROUND

Nanofat is an autologous product prepared mechanically from harvested fat. In nanofat grafting, converters are employed for mechanical emulsification to facilitate fat injection. To date, the study of different converters has received scant attention regarding whether they affect the characteristics of nanofat in terms of the practical applications and indications.

OBJECTIVES

The authors set out to investigate the influence of different internal diameters of converters on biological functionality of nanofat during shuffling.

METHODS

The 3-dimensional finite element method was employed to simulate the process of mechanical emulsification of fat and to research the stress with 5 different converters (3.76 mm, 2.00 mm, 1.20 mm, 1.00 mm, 0.80 mm). An assessment of the morphology of emulsified fat was conducted. Isolated stromal vascular fraction (SVF) was analyzed for cellular components, number, and viability through flowcytometry and live/ dead staining. Adipocytic and angiogenic differentiation assay allowed assessment of differentiation capacity of the SVF.

RESULTS

The smaller the aperture of the converter, the greater the mechanical force on adipose tissue during mechanical emulsification, showing the different macroscopic and microscopic structure of the emulsified fat. No difference in viability or ratio of endothelial progenitor cells and other cells was found. Angiogenic and adipogenic differentiation capacity of the SVF significantly changed in 5 different converters.

CONCLUSIONS

The mechanical emulsification from different apertures of converters exerts different effects of adipose tissue structure, cell content, and multipotency differentiation but not its viability. Converters with different apertures can be selected according to clinical needs.

Characterized the Adipogenic Capacity of Adipose-Derived Stem Cell, Extracellular Matrix, and Microenvironment With Fat Components Grafting

Background: Autologous fat grafting has been a widely used technique; however, the role of adipose-derived stem cells (ASCs), extracellular matrix (ECM), and microenvironment in fat regeneration are not fully understood. Methods: Lipoaspirates were obtained and processed by inter-syringe shifting to remove adipocytes, yielding an adipocyte-free fat (Aff). Aff was then exposed to lethal dose of radiation to obtain decellularized fat (Df). To further remove microenvironment, Df was rinsed with phosphate-buffered saline (PBS) yielding rinsed decellularized fat (Rdf). Green fluorescent protein (GFP) lentivirus (LV-GFP)-transfected ASCs were added to Df to generate cell-recombinant decellularized fat (Crdf). Grafts were transplanted subcutaneously into nude mice and harvested over 3 months. Results: Removal of adipocytes (Aff) didn't compromise the retention of fat grafts, while additional removal of stromal vascular fraction (SVF) cells (Df) and microenvironment (Rdf) resulted in poor retention by day 90 (Aff, 82 ± 7.1% vs. Df, 28 ± 6.3%; p < 0.05; vs. Rdf, 5 ± 1.2%; p < 0.05). Addition of ASCs to Df (Crdf) partially restored its regenerative potential. Aff and Crdf exhibited rapid angiogenesis and M2-polarized macrophages infiltration, in contrast to impaired angiogenesis and M1-polarized inflammatory pattern in Df. GFP + ASCs participated in angiogenesis and displayed a phenotype of endothelial cells in Crdf. Conclusion: Adipose ECM and microenvironment have the capacity to stimulate early adipogenesis while ECM alone cannot induce adipogenesis in vivo. By directly differentiating into endothelial cells and regulating macrophage polarization, ASCs coordinate early adipogenesis with angiogenesis and tissue remodeling, leading to better long-term retention and greater tissue integrity.

Modern Fat Grafting Techniques to the Face and Neck

LEARNING OBJECTIVES

After studying this article, the participant should be able to: 1. Understand age-related changes to the face and neck and pertinent anatomy and discuss important aspects of fat graft harvesting, processing, and infiltration. 2. Recognize key differences between common techniques for fat processing and infiltration and develop a plan for patients based on site-specific facial anatomical zones. 3. Appreciate the utility of fat grafting as an adjunct to other facial rejuvenating procedures such as face lift and blepharoplasty procedures and list the potential complications from fat grafting to the face and neck.

SUMMARY

Fat grafting to the face and neck aids in volume restoration, thereby addressing soft-tissue atrophy associated with the aging face, acquired conditions, or congenital malformations. Often, fat grafting may sufficiently restore facial volume alone or in conjunction with other facial rejuvenation procedures. Facial/neck fat grafting requires a systematic and thoughtful approach, with special care to atraumatic technique. This CME article covers the principles and techniques for modern facial fat grafting to the face and neck. Increasing data support the ability of autologous fat to produce significant and sustainable appearance-related changes. The authors follow the general principles of the Coleman technique for facial fat grafting and have observed tremendous success over the years. Other techniques for facial fat grafting are also discussed including microfat and nanofat processing. As the understanding of facial fat compartments continues to evolve, the authors may better predict fat grafting outcomes following augmentation. Finally, the technique described as "lipotumescence" has been successfully used in the breast and other regions of the body that have radiation damage and is discussed in this article specifically for the face and neck.

The Influence of High and Low Negative Pressure Liposuction and Various Harvesting Techniques on the Viability and Function of Harvested Cells-a Systematic Review of Animal and Human Studies

BACKGROUND

An understanding of fat grafting methodology, techniques and patient-related factors is crucial when considering fat grafting. Multiple factors can influence the success of a fat graft and consequently the outcome of the procedure. The aim of this systematic review is to elucidate the influence of negative pressure and various techniques of fat harvesting on the viability and function of cells, particularly adipocytes and adipose-derived stem cells.

METHODS

We conducted a literature search from 1975 to 2020 using the PubMed bibliography, ScienceDirect, SCOPUS and the Google Scholar databases which produced 168,628 articles on the first pass. After applying all the exclusion criteria by two independent reviewers, we were left with 21 articles (level IV of Oxford Centre for Evidence-Based Studies and Grade C of Grade Practice Recommendation from the American Society of Plastic Surgeons) on which this review is based.

RESULTS

From 11 studies focused on different negative pressures, no one found using high negative pressure advantageous. Summarising 13 studies focused on various harvesting techniques (excision, syringe, and pump-machine), most often equal results were reported, followed by excision being better than either syringe or liposuction.

CONCLUSION

From our systematic review, we can conclude that the low negative pressure seems to yield better results and that the excision seems to be the most sparing method for fat graft harvesting. However, we have to point out that this conclusion is based on a very limited number of statistically challengeable articles and we recommend well-conducted further research.

LEVEL OF EVIDENCE III

This journal requires that authors assign a level of evidence to each article. For a full description of these Evidence-Based Medicine ratings, please refer to the Table of Contents or the online Instructions to Authors www.springer.com/00266 .

Impact of Injection Frequency of Adipose-Derived Stem Cells on Allogeneic Skin Graft Survival Outcomes in Mice

Previous studies indicated that mesenchymal stem cells (MSCs) exhibit immunomodulatory properties in composite tissue allotransplantation. However, due to the high immunogenicity of skin, although the single administration of MSCs improves survival of the skin allotransplant, immune rejection is still inevitable. The aim of our study was to evaluate whether multiple administrations of MSCs would improve immune tolerance in the allogeneic skin graft, compared to that with a single administration in a mouse model. After full-thickness skin allotransplantation on the backs of the mice, the recipient mice were infused with phosphate-buffered saline and isogenic 1.5 × 10⁵/mL adipose-derived stem cells (ADSCs). ADSCs were transplanted into different mice according to the different injection frequencies such as single, once a week, and twice a week. Skin sections were taken on days 7 and 21 post-transplantation in all groups for gene expression and histological studies. ADSCs increased skin allograft survival compared to that in control mice (P < 0.05). Interleukin-6 and tumor necrosis factor-alpha messenger RNA levels were decreased, and the abundance of lymphocytes, based on immunohistochemistry, was also decreased in ADSC-infused mice (P < 0.05). However, among the different ADSC injection frequency groups, multiple ADSC infusion did not improve the survival rate and decreased proinflammatory cytokines and lymphocytes, compared to those with the single administration of ADSCs (P > 0.05). Conversely, the results with single administration were slightly better than those with multiple administrations. Our study demonstrated that ADSCs have the potential for immunomodulation in vivo. However, the results with multiple ADSC administration were not as good as those with single administration, which indicates the complexity of ADSCs in vivo and implying the need for adequate preclinical experimentation.

Salvianolic acid-B improves fat graft survival by promoting proliferation and adipogenesis

Background

Our previous study proved that Salvia miltiorrhiza could enhance fat graft survival by promoting adipogenesis. However, the effect of salvianolic acid B (Sal-B), the most abundant and bioactive water-soluble compound in Salvia miltiorrhiza, on fat graft survival has not yet been investigated.

Objective

This study aims to investigate whether salvianolic acid B could improve fat graft survival and promote preadipocyte differentiation. The underlying mechanism has also been studied.

Methods

In vivo, 0.2 ml of Coleman fat was transplanted into nude mice with salvianolic acid B. The grafts were evaluated by HE and IF at 2 and 4 weeks posttransplantation and by micro-CT at 4 weeks posttransplantation. In vitro, the adipogenesis and proliferative activities of salvianolic acid B were analyzed in cultured human adipose-derived stem cells (h-ADSCs) and 3T3-L1 cells to detect the mechanism by which salvianolic acid B affects graft survival.

Results

In vivo, the weights and volumes of the fat grafts in the Sal-B-treated groups were significantly higher than those of the fat grafts in the control group. In addition, higher fat integrity and more viable adipocytes were observed in the Sal-B-treated groups. In vitro, salvianolic acid B showed the ability to promote 3T3-L1 and h-ADSC proliferation and adipogenesis.

Conclusions

Our in vitro experiments demonstrated that salvianolic acid B can promote the proliferation of adipose stem cells and enhance the differentiation of adipose stem cells. Simultaneously, in vivo experiments showed that salvianolic acid B can improve the survival rate of fat transplantation. Therefore, our research shed light on the potential therapeutic usage of salvianolic acid B in improving the survival rate of fat transplantation.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13287-021-02575-4.

The Effects of Lipoaspirate-Derived Fibrous Tissue on Survival Quality and Mechanical Property of Fat Grafts

BACKGROUND

Fibrous connective tissue (referred to as fiber) in lipoaspirates would be discarded before lipotransfer in case of cannula blockage. However, the fiber contains extracellular matrix which provide structure support and is rich in stromal vascular fractions (SVFs). Removal of the fiber might theoretically affect the survival quality and mechanical properties of fat grafts. But there is few evidence in vivo and vitro about how the fiber affects the fat grafts.

OBJECTIVE

To assess the effect of fibers on the survival quality and mechanical property of fat grafts.

METHODS

The SVFs in both fat and fiber were obtained by collagenase digestion for cells counting and comparison. Three groups were designed according to the different proportions of fat and fiber: the fat group (100% fat), the mixed group (50% fat, 50% fiber in volume ratio), and the fiber group (100% fiber). Three groups of grafts were transplanted in vivo to evaluate the differences in volume retention rate, histological characteristics and mechanical properties.

RESULTS

The amount of SVF cells in fibers (3.47 ± 1.49 × 104 cells/mL) was significantly lower than that in fat (12.3 ± 4.95 × 104 cells/mL) (P < 0.05). Grafts in the mixed group and the fiber group showed an increase of volume retention at week 4, but the fiber content showed no significant effects on the volume retention of grafts in three groups at week 12. Elasticity modulus of grafts in the fat group was higher than that in the fiber group and the mixed group at week 4 and 8, the fiber content showed no significant effects on the elasticity modulus of grafts in three groups at week 12. The addition of the fiber reduced the inflammation, cysts, fibrosis, and capillaries density of the grafts.

CONCLUSIONS

There were few SVF cells in the fiber. When it was mixed with fat in different proportions and transplanted in vivo, the content of fiber showed no significantly different effects on the long-term volume retention and mechanical property of fat grafts. Due to the risk of blockage, it is recommended to discard the fiber in lipoaspirates.

Effects of Administration Route of Adipose-Derived Stem Cells on the Survival of Allogeneic Skin Grafts in Mice

BACKGROUND

Composite tissue allotransplantation presents considerable potential for defective tissue reconstruction. However, the high immunogenicity of the allogeneic skin grafts can cause acute rejection. Adipose-derived stem cells (ADSCs) reportedly have an immunomodulation potential, which may improve the survival of allogeneic skin grafts. However, there is currently no consensus on administration route of ADSCs. This study compared the effectiveness of local injection vs intravenous (IV) administration of ADSCs in improving the survival of allogenic skin grafts in mice.

METHODS

BALB/c and C57BL/6 mice were used as skin graft donors and recipients, respectively. Mice were divided into 3 groups for IV injection of ADSCs (IV group) or phosphate-buffered saline (PBS; control), or for local injection in the fascial layer of the recipient bed (FL group). After allogeneic skin transplantation, 0.1 mL of PBS alone or with 1.5 × 10⁵ ADSCs was immediately injected. The grafts were histologically evaluated on days 7 and 14 postoperation.

RESULTS

The graft necrotic area was significantly smaller in the IV and FL groups than in the control group. Additionally, the grafts in these 2 groups exhibited decreased interleukin 17/6, tumor necrosis factor-α, and interferon-γ messenger mRNA levels; inflammatory changes; and cluster of differentiation 4 expression, and increased expression of vascular endothelial growth factor expression (P < .05). However, these 2 groups did not significantly differ (P > .05).

CONCLUSIONS

ADSCs increased the survival of allogeneic skin grafts in mice regardless of IV or FL route of administration, and this effect is likely through anti-inflammatory and angiogenic effects of ADSCs.

Effects of macrophage regulation on fat grafting survival: Improvement, mechanisms, and potential application-A review

BACKGROUND

Autologous fat grafting has become a popular tool in plastic surgery to solve soft tissue defects and achieve skin rejuvenation, but the volume loss after transplantation remains a disturbing problem. In recent years, some new strategies have improved the outcome to some extent, but the fat graft retention is still far from ideal, so there remains a wide development prospect in this field. Macrophages are closely related to the local microenvironment and tissue regeneration, and their role in fat grafting has been increasingly highlighted.

AIMS

This article was aimed to review the efficacy, possible mechanisms, and potential application of macrophage regulation on fat grafting, as well as concerns and future perspectives of this filed.

METHODS

A retrospective review of the published data was conducted.

RESULTS

Most studies indicated that up-regulating M2 macrophages during fat grafting would improve fat retention via promoting neovascularization. M2 macrophages could secrete several pro-angiogenic factors, accelerate extracellular matrix (ECM) remodeling, and directly function on endothelial cells to encourage vascular expansion. In addition, macrophages could influence the proliferation, apoptosis, and adipogenic differentiation of preadipocytes.

CONCLUSIONS

During autologous fat grafting, appropriately regulating macrophages may become a promising method to increase fat retention. Nevertheless, the M2 macrophage polarizing agents, treatment opportunity, and contraindications require further discussion. We hope our work could promote more in-depth studies in this field, and we are looking forward to a standard procedure for the macrophage therapy in clinical practice.

Impact of Fat Graft Thickness and Harvesting Technique on Adipocyte Viability in a New Porcine Experimental Model: An Immunohistochemical Analysis

BACKGROUND

Autologous fat grafting (AFG) has been employed in surgical practice as a filling method. However, controversies remain on the specifics of this technique. So far, few relevant experimental large animal studies have objectively assessed factors related to AFG integration.

OBJECTIVES

This study utilized an experimental, medium-sized animal model to compare the feasibility of AFG collected employing 2 different techniques with instruments of distinct thicknesses.

METHODS

Twenty minipigs (Sus scropha domesticus) were subjected to AFG harvesting via en bloc resection utilizing 3- (Group I) and 5-mm-diameter (Group II) round punch blades (PBs) and liposuction (LS) with 3- (Group III) and 5-mm-diameter cannulas (Group IV). Both samples were grafted intramuscularly (biceps femoralis). Hematoxylin and eosin staining was employed to identify intact adipocytes, fat necrosis, fibrosis, inflammation, and oil cysts. Immunohistochemical staining (perilipin-A, tumor necrosis factor alfa, and cluster of differentiation number 31) was utilized to quantify the feasibility of adipocytes, tissue necrosis, and neoangiogenesis, respectively.

RESULTS

Hematoxylin and eosin analysis showed that fat necrosis and histiocyte presence were significantly lower in the AFG harvested utilizing a PB than in LS. For perilipin-A, a statistical difference was observed between subgroups I and III (P = 0.001) and I and IV (P = 0.004). Instrument diameter had no effect on graft integration in comparisons between groups II and III (P = 0.059) and II and IV (P = 0.132).

CONCLUSIONS

In this experimental study, fat collected utilizing a PB demonstrated higher adipocyte viability than fat collected with LS. The diameter of the collection instruments, whether PB or LS, had no effect on graft integration.

Water jet-assisted lipoaspiration and Sepax cell separation system for the isolation of adipose stem cells with high adipogenic potential

INTRODUCTION

Water jet-assisted liposuction has gained popularity due to favourable fat grafting outcomes. In this study, we compared stem cells obtained from fat isolated with manual or the water jet-assisted procedure.

METHODS

Liposuction of abdominal fat was performed using the two methods on each donor (n = 10). Aspirate samples were collagenase digested and the isolated cells seeded in vitro prior to proliferation, adipogenic differentiation and angiogenic activity analyses.

RESULTS

Cells from either procedure proliferated at similar rates and exhibited a similar colony-forming ability. The cells expressed stem cell markers CD73, CD90 and CD105. In the water jet cell preparations, there were higher numbers of cells expressing CD146. Robust adipogenic differentiation was observed in cultures expanded from both manual and water jet lipoaspirates. Gene analysis showed higher expression of the adipocyte markers aP2 and GLUT4 in the adipocyte-differentiated water jet cell preparations, and ELISA indicated increased secretion of adiponectin from these cells. Both cell groups expressed vasculogenic factors and the water jet cells promoted the highest levels of in vitro angiogenesis. Given these positive results, we further characterised the water jet cells when prepared using an automated closed cell processing unit, the Sepax-2 system (Cytiva). The growth and stem cell properties of the Sepax-processed cells were similar to the standard centrifugation protocol, but there was evidence for greater adipogenic differentiation in the Sepax-processed cells.

CONCLUSIONS

Water jet lipoaspirates yield cells with high adipogenic potential and angiogenic activity, which may be beneficial for use in cell-assisted lipotransfers.

Direct Conversion of Human Fibroblasts into Adipocytes Using a Novel Small Molecular Compound: Implications for Regenerative Therapy for Adipose Tissue Defects

There is a need in plastic surgery to prepare autologous adipocytes that can be transplanted in patients to reconstruct soft tissue defects caused by tumor resection, including breast cancer, and by trauma and other diseases. Direct conversion of somatic cells into adipocytes may allow sufficient functional adipocytes to be obtained for use in regeneration therapy. Chemical libraries of 10,800 molecules were screened for the ability to induce lipid accumulation in human dermal fibroblasts (HDFs) in culture. Chemical compound-mediated directly converted adipocytes (CCCAs) were characterized by lipid staining, immunostaining, and qRT-PCR, and were also tested for adipokine secretion and glucose uptake. CCCAs were also implanted into mice to examine their distribution in vivo. STK287794 was identified as a small molecule that induced the accumulation of lipid droplets in HDFs. CCCAs expressed adipocyte-related genes, secreted adiponectin and leptin, and abundantly incorporated glucose. After implantation in mice, CCCAs resided in granulation tissue and remained adipose-like. HDFs were successfully converted into adipocytes by adding a single chemical compound, STK287794. C/EBPα and PPARγ were upregulated in STK287794-treated cells, which strongly suggests involvement of these adipocyte-related transcription factors in the chemical direct conversion. Our method may be useful for the preparation of autogenous adipocytes for transplantation therapy for soft tissue defects and fat tissue atrophy.

[Research progress of adipose-derived stem cells in skin scar prevention and treatment]

Objective

To review the research progress of adipose-derived stem cells (ADSCs) in skin scar prevention and treatment.

Methods

The related literature was extensively reviewed and analyzed. The recent in vitroand in vivo experiments and clinical studies on the role of ADSCs in skin scar prevention and treatment, and the possible mechanisms and biomaterials to optimize the effect of ADSCs were summarized.

Results

As demonstrated by in vitro and in vivo experiments and clinical studies, ADSCs participate in the whole process of skin wound healing and may prevent and treat skin scars by reducing inflammation, promoting angiogenesis, or inhibiting (muscle) fibroblasts activity to reduce collagen deposition through the p38/mitogen-activated protein kinase, peroxisome proliferator activated receptor γ, transforming growth factor β ₁/Smads pathways. Moreover, bioengineered materials such as hydrogel from acellular porcine adipose tissue, porcine small-intestine submucosa, and poly (3-hydroxybutyrate-co-hydroxyvalerate) scaffold may further enhance the efficacy of ADSCs in preventing and treating skin scars.

Conclusion

Remarkable progress has been made in the application of ADSCs in skin scar prevention and treatment. While, further studies are still needed to explore the application methods of ADSCs in the clinic.

Differences of embedding adipose-derived stromal cells in natural and synthetic scaffolds for dermal and subcutaneous delivery

Background

In recent years, adipose-derived stromal cells (ASCs) have been heavily studied for soft tissue regeneration, augmentation, and dermal wound healing.

Methods

In this review, we investigated the trends in injectable scaffolds for ASC delivery in the dermis, and injectable or implantable scaffolds for ASC delivery in the subcutis. A total of 547 articles were screened across three databases; of these, 22 studies were found to be eligible and were included. The scaffolds were subdivided and analyzed based on their tissue placement (dermis or subcutis), delivery method (injected or implanted), and by the origin of the materials (natural, synthetic, and combinatory).

Results

ASCs embedded in scaffolds generally showed improved viability. Neovascularization in the transplanted tissue was greater when undifferentiated ASCs were embedded in a combinatory scaffold or if differentiated ASCs were embedded in a natural scaffold. ASCs embedded in natural materials underwent more adipogenic differentiation than ASCs embedded in synthetic scaffolds, indicating an etiologically unknown difference that has yet to be described. Increased mechanical strength of the scaffold material correlated with improved outcome measurements in the investigated studies. Wound healing studies reported reduced healing time in all except one article due to contraction of the control wounds.

Conclusions

In future clinical trials, we recommend embedding ASCs in injectable and implantable scaffolds for enhanced protection, retained viability, and improved therapeutic effects.

Trial registration

This review was registered with PROSPERO: ID=CRD42020171534.

Graphical abstract

The use of scaffolds as a vehicle for ASC delivery generally improved cell viability, angiogenesis, and wound healing in vivo compared to utilizing ASCs alone. ASCs embedded in natural materials induced more adipogenesis than ASCs embedded in synthetic materials. Adipogenic-induced ASCs further increased this effect. The included studies indicate that the seeded scaffold material influences the differentiation of ASCs in vivo. All studies investigating the mechanical strength of ASC scaffolds reported improved outcome measurements with improved mechanical strength. The results suggest that scaffolds, in general, are favorable for ASC delivery. We recommend initiating clinical studies using scaffolds based on mechanical properties and tunability to improve ASC viability. For fat regeneration, natural scaffolds are recommended.

Lipotransfer Strategies and Techniques to Achieve Successful Breast Reconstruction in the Radiated Breast

Radiation therapy is frequently a critical component of breast cancer care but carries with it side effects that are particularly damaging to reconstructive efforts. Autologous lipotransfer has the ability to improve radiated skin throughout the body due to the pluripotent stem cells and multiple growth factors transferred therein. The oncologic safety of lipotransfer to the breasts is demonstrated in the literature and is frequently considered an adjunctive procedure for improving the aesthetic outcomes of breast reconstruction. Using lipotransfer as an integral rather than adjunctive step in the reconstructive process for breast cancer patients requiring radiation results in improved complication rates equivalent to those of nonradiated breasts, expanding options in these otherwise complicated cases. Herein, we provide a detailed review of the cellular toxicity conferred by radiotherapy and describe at length our approach to autologous lipotransfer in radiated breasts.

Fat grafts enriched with adipose-derived stem cells

Autologous fat grafts are widely used in soft-tissue augmentation and reconstruction. To reduce the unpredictability of fat grafts and to improve their long-term survival, cell-assisted lipotransfer (CAL) was introduced. In this alternative method, autologous fat is mixed and grafted with stromal vascular fraction cells or adipose-derived stem/stromal cells (ASCs). In regenerative medicine, ASCs exhibit excellent therapeutic potential and are also simple to harvest. Although the efficacy of CAL has been demonstrated in experimental and clinical research, studies on its safety in terms of oncologic risk have reported inconclusive results. In order to establish CAL as a viable stem cell therapeutic approach, it will be necessary to demonstrate its oncologic safety in basic and clinical studies. Doing so could transform the paradigm of clinical strategy and practice for the treatment of a wide variety of diseases.

How Fat Grafting Works

Fat grafting has been shown to improve diseased soft issue. Although the mechanism behind fat grafting’s regenerative properties is currently debated, published studies agree that there is an associated vasculogenic effect. A systematic literature review was conducted to elucidate the biochemical pathways responsible for establishing neo-vasculature to grafted fat.

Adipogenesis for soft tissue reconstruction

PURPOSE OF REVIEW

It has been increasingly common to use adipose tissue for regenerative and reconstructive purposes. Applications of autologous fat transfer and different stem cell therapies have significant limitations and adipose tissue engineering may have the potential to be an important strategy in the reconstruction of large tissue defects. A better understanding of adipogenesis will help to develop strategies to make adipose tissue more effective for repairing volumetric defects.

RECENT FINDINGS

We provide an overview of the current applications of adipose tissue transfer and cellular therapy methods for soft tissue reconstruction, cellular physiology, and factors influencing adipogenesis, and adipose tissue engineering. Furthermore, we discuss mechanical properties and vascularization strategies of engineered adipose tissue, and its potential applications in the clinical settings.

SUMMARY

Autologous fat tissue transfer is the standard of care technique for the majority of surgeons; however, high resorption rates, poor perfusion within a large volume fat graft and widely inconsistent graft survival are the main limitations. Adipose tissue engineering is a promising field to reach the first goal of producing adipose tissue which has more predictable survival and higher graft retention rates. Advancements of scaffold and vascularization strategies will contribute to metabolically and functionally more relevant adipose tissue engineering.

Extracellular vesicles derived from human adipose-derived stem cells promote the exogenous angiogenesis of fat grafts via the let-7/AGO1/VEGF signalling pathway

Extracellular vesicles (EVs) derived from human adipose-derived stem cells (hADSCs) possess the proangiogenic potential for ischaemic diseases. Thus, our study aimed to evaluate the therapeutic effects of hADSC-EVs on fat grafting and explore the mechanism of hADSC-EVs promoting angiogenesis. The EVs released by hADSCs incubated under normal or hypoxic conditions were employed to supplement fat grafting in a nude mouse model. The proliferation, migration, tube formation and vascular endothelial growth factor (VEGF) secretion of vascular endothelial cells co-cultured with two kinds of hADSC-EVs were analysed. MicroRNA sequencing was performed to reveal the species and content of microRNAs in hADSC-EVs, the key microRNAs were blocked, and their effect in promoting angiogenesis was detected via above protocols as a reverse proof. The results demonstrate that hADSC-EVs could improve the survival of fat grafts by promoting exogenous angiogenesis and enhance the proliferation, migration, tube formation and VEGF secretion of vascular endothelial cells. In addition, the pro-angiogenic effect of hADSC-EVs in vivo and vitro could be enhanced by hypoxic pre-treatment. We found that the let-7 family, a kind of hypoxic-related microRNA, is enriched in hypoxic hADSC-EVs that contribute to angiogenesis via the let-7/argonaute 1 (AGO1)/VEGF signalling pathway.