Adipose Tissue-Derived Mesenchymal Stem Cells : A Novel Therapy in Orthopedics

Background: Mesenchymal stem cells can differentiate into a variety of cell types. They have the ability to release bioactive molecules, making them attractive tools in cell-based therapies. Adipose tissue is an ideal source of autologous mesenchymal stem cells for its abundance and easy access. Mesenchymal stem cells are routinely obtained enzymatically from lipoaspirate as stromal vascular fraction. Objectives: The aim of this review is to investigate the advantages of adipose derived stem cells in orthopedic application. Methods: Randomised controlled trials (RCTs) and non-RCTs, in addition to cohort and case control studies, as well as case series were included. Search language was restricted to English and time starting from year 2012. Only published papers were eligible. Results: Thirteen articles were included in the review, they consisted of 1 RCT, 4 nRCTs, 1 prospective comparative study, 1 longitudinal cohort study, 2 case control studies, 3 case series and one case report. The number of patients injected with stem cells ranged between 12 and 1128. A total of 1482 patients were treated with adipose derived stem cells Conclusion: The use of adipose derived stem cells had shown to be safe and effective in bone and cartilage repair.


Introduction
Regenerative medicine is an emerging field of multidisciplinary science.This evolving field is taking over the recent medical era as it combines growth factors, biomaterials, and stem cells to repair failing organs relying on fast and efficient tissue growth [1,2].Regenerative medicine is being applied in orthopedics.It is being used to repair bone, tendon and cartilage damage [3].
Regenerative medicine is divided into two different techniques, the first is cell therapy and the second is tissue engineering.In cell therapy, a cell suspension is injected into the damaged tissue or blood circulation.This is used to repair damaged tissues to regain their function.However, this approach is insufficient to replace organs or regenerate large tissue defects.An alternative approach is tissue engineering.Yet, it is more complex and it is being barely used in clinical practice due to the issue of vascularization [3].
In order to overcome the above hurdles, alternative sources of MSCs were sought.Adipose tissue of abdomen, thigh and hips serves as an ideal source of mesenchymal stem cells because of its availability and accessibility [26,27,29,30,40,49].Adipose tissue derived stem cells are being employed in regenerative medicine due to their ability to differentiate into bone, tendon, cartilage, muscles and other tissues.

Non-enzymatic Isolation
Adipose tissue, or lipoaspirate, obtained from liposuction is digested with collagenase to release MSCs called adipose tissuederived stem cell (ASCs).The ASCs undergo several rounds of centrifugation and dilution through which collagenase is washed off and the remaining product is the stromal vascular fraction (SVF) [35,[50][51][52][53][54].SVF has been used as a source of cells useful for tissue regeneration.The most common isolation technique to obtain SVF is the enzymatic digestion which consists of washing, treatment with enzymes, erythrocyte lysis, and cryopreservation or culture expansion [55][56][57][58][59][60][61][62][63][64].This technique is costly and might jeopardize the safety as well as the efficacy of the lipoaspirates [4,65].When compared to enzymatically derived MSCs, mechanically derived MSCs have superior differentiation potential with larger secretome content and more diverse exosome content without disruption of vascular stroma [66,67].This method is purely mechanical with no chemical additives used; thus, showing promising results that power the method of nonenzymatic harvesting of stem cells derived adipose tissue [19,[68][69][70][71][72].

Application of Adipose Derived Stem Cells in Orthopedics
The aim of this review is to investigate the advantages of adipose derived stem cells in orthopedic application.Randomised controlled trials (RCTs) and non-RCTs (nRCTs), in addition to cohort and case control studies, as well as case series were included.Search language was restricted to English and time starting from year 2012.Only published papers were eligible.

Rheumatoid Arthritis
Adipose derived stem cells have shown therapeutic effect in vitro [85].They inhibit T-cell proliferation, produce inflammatory cytokines, and generate antigen-specific regulatory T-cells.Thus, they suppress responses of collagen II-reactive T-cells from patients with rheumatoid arthritis [85].Alvaro-Gracia JM et al. conducted a randomized, placebo-controlled trial to assess the safety and tolerability of the intravenous administration of allogeneic expanded adipose-derived stem cells in patients with refractory rheumatoid arthritis.Three cohorts received treatment with doses of 1, 2 and 4 million cells/kg at days 1, 8 and 15 while the fourth cohort received placebo.They concluded that the intravenous administration of adipose derived stem cells was well tolerated and was not associated with dose-related toxicity.Signs for a potential therapeutic effect of these cells were observed [73].

Osteoarthritis
Intra-articular injection of adipose derived stem cells was shown to reduce synovitis, osteophyte formation, and cartilage degeneration in animal models [86,87].Pers YM et al conducted a clinical trial to assess the safety and efficacy of intra-articular injection of autologous ASCs in patients with knee osteoarthritis.Eligible patients were allocated to three treatment groups (no placebo) with different doses (2, 10 and 50 million cells).They concluded that the technique was safe and well tolerated in patients with knee osteoarthritis [74].
Michalek J et al. carried out a case control study to evaluate the safety and clinical efficacy of autologous stromal vascular fraction (SVF) cells in patients with grade 2-4 degenerative osteoarthritis mainly of large joints (hip and knee) in addition to medium joints (elbow and wrist) as well as small joints (hand and foot).Single injection of adipose-derived SVF cells was given intra-articularly or peri-articularly to the synovial stromal tissue in close proximity of the joint.The technique was safe and clinically effective.This was demonstrated by the improved quality of life of patients [67].
Koh YG et al. carried out a prospective comparative study during which patients with a single International Cartilage Repair Society grade III/IV symptomatic cartilage defect on the femoral condyle were randomized into two groups.The first group received adipose derived stem cells with fibrin glue and micro fracture treatment whereas the second group received micro fracture treatment alone.The group that received stem cells and micro fracture with fibrin glue had improved radiologic, pain and symptom scores with no differences in activity, sports, or quality-of-life scores in comparison to the other group [78].
Jo CH et al. conducted a phase I/II clinical trial to assess the safety and the efficacy of intra-articular injection of autologous adipose tissue derived mesenchymal stem cells in patients with knee osteoarthritis.Phase I consisted of three cohorts; with three patients each.Patients in each dose group received 10, 50 and 100 million cells in 3 mL of saline.Three patients in each cohort were followed up for 28 days after injection.A safety review was done and phase II was started including 9 patients receiving 100 million cells.The authors concluded that intra-articular injection of 100 million adipose stem cells into the osteoarthritic knee improved function and reduced knee pain without causing adverse events.Radiological, histological and arthroscopic measures showed decreased articular cartilage defects by regeneration of hyaline-like articular cartilage [76].
Bui KH et al. performed a clinical trial to evaluate the efficiency and side-effects associated with the injection of SVF (obtained from adipose tissue of the belly) and platelet rich plasma in knee osteoarthritis.All patients had improved joint function and reduced pain scores.MRI findings showed significant improvements and increased thickness of cartilage layer.There were no complications with respect to infection or graft rejection [77].
Koh YG et al. described a series of elderly patients with knee osteoarthritis who received injections of adipose-derived stromal vascular cells after arthroscopic lavage.They concluded that the technique was effective in reducing pain, cartilage healing and improving function [81].
Pak J et al. carried out a retrospective cohort study in which patients were treated with autologous adipose derived stem cells with platelet-rich plasma for hip, knee, low back and ankle procedures.They concluded that the technique was safe when used as percutaneous local injections and there were no neoplastic complications [79].
Koh YG et al. conducted a case control study to assess the safety and effectiveness of mesenchymal stem cells (MSCs) derived from the infrapatellar fat pad when percutaneously injected into arthritic knees.Patients in the study group received a mean of 1.89 million stem cells with 3.0 mL of platelet-rich plasma and injected in the selected knees of patients while patients in the control group received platelet rich plasma that does not contain stem cells.There were no complications such as infection, fever, hematoma, tissue hypertrophy, adhesion formation observed among the study subjects.The authors concluded that the therapy reduced pain and improved patients' function [80].

Lateral Epicondylosis
Lee SY et al. evaluated the safety and efficacy of allogeneic adipose-derived mesenchymal stem cells for the treatment of lateral epicondylosis.Allogenic adipose derived stem cells were mixed with fibrin glue and injected into the hypoechoic common extensor tendon lesions under ultrasound guidance.Patients had reduced pain scores, improved elbow performance scores and decreased tendon defects.Within 52 weeks after the injection [77].

Chondromalacia Patellae
Pak J et al. evaluated the injection of adipose derived stem cells in series of three patients with Chondromalacia Patellae.The stromal vascular fraction was separated from the lipoaspirates by centrifugation after treatment with collagenase.The stem-cell-containing stromal vascular fraction was mixed with calcium chloride-activated platelet rich plasma and hyaluronic acid.The mixture was injected under ultrasonic guidance into the retro-patellar joints of the patients.The pain scores improved 50-70% one month after the injection and 80-90% after three months.The pain improvement persisted over one year.There were no serious side effects.The repeated magnetic resonance imaging scans at three months showed restoration of the damaged tissues (softened cartilages) on the patellae-femoral joints [82].

Osteonecrosis of Femoral Head
Pak J et al. evaluated the effect of adipose tissue-derived stem cells and platelet-rich plasma on to the regeneration of medullary bone-like tissue and long-term reduction of pain in two patients with femoral head osteonecrosis.Stem cells were obtained from lipoaspirates of lower abdominal subcutaneous adipose tissue.The stromal vascular fraction was separated from the lipoaspirates by centrifugation after treatment with collagenase.The stem-cell-containing stromal vascular fraction was mixed with calcium chloride-activated platelet rich plasma and hyaluronic acid.The mixture was injected into the affected hip.The diseased hip was re-injected with calcium chlorideactivated platelet rich plasma on weekly basis for 4 weeks.The physical therapy testing, visual analog scale score, and Harris Hip score of the two patients improved after the treatment.Both patients showed improvement in their MRI scans, evidenced by positive T1 signal changes consistent with medullary bone regeneration.Moreover, the long-term reduction in hip pain was correlated with the MRI findings indicative of bone regeneration.The two cases demonstrated the presence of sustained, regenerated medullary bone-like tissue in severely necrotic femoral heads and suggest that this simple and minimally invasive procedure may be a promising therapy for patients with femoral head osteonecrosis [83].
Another report by Pak J et al. described a single case of early stage a vascular necrosis of the femoral head.Adipose derived stem cells containing stromal vascular fraction were mixed with platelet rich plasma and hyaluronic acid.The mixture was injected into the diseased hip under ultrasound guidance.The affected hip was reinjected weekly with additional platelet rich plasma for 4 weeks.The patient was followed-up MRI scans at 3, 18, and 21 months after treatment.Visual Analogue Scale, Walking Index, Functional Rating Index, Harris Hip Score, and Range of Motion assessments were also noted.The patient's severe hip pain was considerably improved at 3 months after treatment.Pain scores, range of motion and MRI at 18 and 21 months post treatment indicated complete resolution of a vascular necrosis of the femoral head [84][85][86][87].

Conclusion
The use of adipose derived stem cells had shown promising results in bone and cartilage repair.Further clinical trials are needed to confirm the short and long term efficacy of adipose derived stem cells in various orthopedic applications.

Table 1 :
Application of adipose derived stem cells in orthopedics.