Autologous stem cell transplantation for treatment of rectovaginal fistula in perianal Crohn's disease: a new cell-based therapy

Human adipose-derived stem cells: isolation, characterization and applications in surgery

The ideal stem cell for use in functional tissue engineering needs to be abundantly available, harvested with minimal morbidity, differentiated reliably down various pathways and able to be transplanted safely and efficaciously. Adult human adipose tissue contains a population of mesenchymal stem cells, termed 'adipose-derived stem cells' (ASC), which seem to fulfil most, if not all, of these criteria. ASC can be harvested readily, safely, and in relative abundance by modern liposuction techniques. They are capable of differentiating into other mesenchymal tissue types, including adipocytes, chondrocytes, myocytes and osteoblasts. They also show angiogenic properties, with recent evidence of a potential role in healing radiotherapy-damaged tissue, possibly due to their secretion of vascular endothelial growth factor. Similarly, they may have a role in healing chronic wounds, and as such are being investigated in phase 1 trials for their ability to aid healing of recurrent Crohn's fistulae. Subsequently they have a wide range of potential clinical uses in all fields of surgery. This article reviews the current and potential clinical applications of ASC in relation to surgery, as well as methods for their isolation, differentiation and molecular characterization.

Early Translation of Adipose-Derived Cell Therapy for Cardiovascular Disease

Over the past decade, cell therapy has emerged as a new approach to reversing myocardial ischemia. Several types of adult stem cells have been studied in both preclinical and clinical conditions for this purpose: bone marrow cells, circulating cells, and myoblasts. Nevertheless, the quest for the ideal “anti-ischemic” cell is still ongoing. Recently, the existence of a population of stem cells located in adipose tissue (adipose-derived stem cells) has been observed. These are able to differentiate into multiple cell lineages including cardiomyocytic differentiation. In this review we discuss the basic principles of adipose-derived stem cells (types and characteristics, harvesting, and expansion), the initial experimental studies, and the currently ongoing clinical trials.

Treatment of enterocutaneous fistula in Crohn's Disease with adipose-derived stem cells: a comparison of protocols with and without cell expansion

BACKGROUND

Expanded adipose-derived stem cells (ASC) have been shown to be effective in treating Crohn's patients with enterocutaneous fistulas. It is possible that unexpanded cells corresponding to the stromal vascular fraction (SVF) may also be effective.

MATERIALS AND METHODS

A subpopulation of patients from a previous proof-of-concept phase I study with enterocutaneous fistulas received autologous expanded ASCs. The same selection criteria for inclusion were applied to patients who underwent SVF implantation to treat enterocutaneous fistulas. After tract curettage, cell suspensions (either SVF cells from lipoaspirate or expanded ASCs) were injected into the tract walls, and the fistulous tract was sealed with fibrin adhesive (with or without cells).

RESULTS

In the series that received ASCs, four fistulas could be evaluated, and cure was achieved in three out of four cases. In the series that received SVF cells, four fistulas were evaluated, with cure achieved in one out of four cases.

CONCLUSIONS

Although a comparison of case series cannot be considered firm evidence, a therapeutic protocol that uses expansion prior to implantation does seem to be more effective than one that uses SVF cells directly from a lipoaspirate sample.

[Prevalence of anal diseases after Scopinaro's biliopancreatic bypass for super-obese patients]

INTRODUCTION

Biliopancreatic diversion by Scopinaro (BD) is a mixed (malabsortive and restrictive) bariatric technique that is successful in achieving long lasting weight lost in super obese patients. In fact, the diarrhoea (steatorrhea) that is expected after any malabsortive technique can sometimes cause significant nutritional changes and anal disease: these patients are frequently referred to our coloproctology outpatient clinic due to haemorrhoids, fissures, anal sepsis and fistula basically due to changes in quality and quantity of their faeces. The aim of this paper is to find out not only the prevalence of anal disease in our series of super obese surgical patients but also to compare the incidence between the two surgical techniques we perform in our department.

MATERIAL AND METHOD

We analyzed 263 consecutive patients operated on BD of Scopinaro (50-200 cm) and modified-BD (75-225 cm) in our Department. Patients who had previously suffered from anal surgery were excluded.

RESULTS

There were 45 patients (18%) who suffered from anal problems of which 38 cases (84.4%) were BD-S and only 7 cases with BD-M complained of anal disorders (p < 0.05). Overall, at the 18th month review, the mean number of motions per day was 3.5 (range, 1-15). Patients with BD-S had 5 motions per day as a mean. The mean number of motions for BD-M was 2. The frequency order of anal pathology observed was: anal fissure, haemorrhoids, abscess and fistula.

CONCLUSIONS

Higher incidence of anal pathology after BD of Scopinaro is another factor to take into account to avoid performing classic Scopinaro BD as opposed to modified BD for the treatment of morbid super obesity. It is mandatory to be conservative when facing anal problems in these patients, and firstly we must modify eating habits and the nutritional status. Surgery must be highly respectful to anal sphincters to avoid incontinence.

Inflammatory bowel disease: Moving toward a stem cell-based therapy

The incidence and prevalence of Crohn's disease (CD) and ulcerative colitis (UC), the two major forms of inflammatory bowel diseases (IBD), are rising in western countries. The modern hygienic lifestyle is probably at the root of a disease where, in genetically susceptible hosts, the intestinal commensal flora triggers dysregulated immune and inflammatory responses. Current therapies ranging from anti-inflammatory drugs to immunosuppressive regimens, remain inadequate. Advances in our understanding of the cell populations involved in the pathogenetic processes and recent findings on the regenerative, trophic and immunoregulatory potential of stem cells open new paths in IBD therapy. Hematopoietic and mesenchymal stem cells are catalyzing the attention of IBD investigators. This review highlights the pivotal findings for stem cell-based approaches to IBD therapy and collects the encouraging results coming in from clinical trials.

Current considerations in the management of rectovaginal fistula from Crohn's disease

Rectovaginal fistulas are dreaded complications of Crohn's disease. Accurate assessment is essential for planning management. Treatment options range from observation to medical therapeutics to the need for surgical intervention. Ultimately, establishing reasonable expectations is mandatory when treatment algorithms are considered. In this article, we review the evaluation of these fistulas and the current options to consider in the treatment of Crohn's related rectovaginal fistula.

Inflammatory bowel disease: Moving toward a stem cell-based therapy

The incidence and prevalence of Crohn's disease (CD) and ulcerative colitis (UC), the two major forms of inflammatory bowel diseases (IBD), are rising in western countries. The modern hygienic lifestyle is probably at the root of a disease where, in genetically susceptible hosts, the intestinal commensal flora triggers dysregulated immune and inflammatory responses. Current therapies ranging from anti-inflammatory drugs to immunosuppressive regimens, remain inadequate. Advances in our understanding of the cell populations involved in the pathogenetic processes and recent findings on the regenerative, trophic and immunoregulatory potential of stem cells open new paths in IBD therapy. Hematopoietic and mesenchymal stem cells are catalyzing the attention of IBD investigators. This review highlights the pivotal findings for stem cell-based approaches to IBD therapy and collects the encouraging results coming in from clinical trials.

[Stem cell transplantation in the treatment of gastrointestinal diseases]

The stem cells with self-renewal ability are capable to form one or more cell types. They will be in the target of cell and gene therapy because of their multipotency and easy retrieval. Application of adult mesenchymal, neuronal, epidermal and haematopoietic stem cell can be favourable in the treatment of cardiac (myocardial infarction), bone (osteoarthritis), neurological (Parkinson's, Alzheimer's) and hematological (hemophilia, thrombocytopenia) disorders. Authors summarize the knowledge in connection with their application in the therapy of gastrointestinal diseases. Haematopoietic stem cell transplantation has been successful for the treatment of refractory Crohn's disease, as well as in selected group of celiac patients. Mesenchymal stem cell transplantation has been proved beneficial in the prevention of liver fibrotic process. It will gain more grounds in the treatment of autoimmune liver diseases: autoimmune hepatitis, primary biliary cirrhosis and primary sclerosing cholangitis in the future. Well-designed, multicentric, prospective studies are needed to confirm the results of case reports and clinical studies with small group of patients.

Adipose-derived cells

Heart failure is by far the most common cause of hospitalization in Western countries, with onerous economic consequences. Cell therapy holds great promise for use in tissue regeneration and is increasingly used in an effort to improve outcomes in cardiac disease. Recently it has been shown that adipose tissue, in addition to committed adipogenic, endothelial progenitor cells and pluripotent vascular progenitor cells, also contains multipotent cell types (adipose-derived stem cells, ADSCs) that, in cell culture conditions, have shown to have an impressive developmental plasticity including the ability to undergo multilineage differentiation and self-renewal. ADSCs express multiple CD marker antigens similar to those observed on MSCs and are also capable of secreting a large number of angiogenesis-related cytokines, including vascular endothelial growth factor, granulocyte/macrophage colony stimulating factor, stromal-derived factor-1alpha, and hepatocyte growth factor. Adipose tissue can be harvested in large quantities with minimal morbidity in several regions of the body and, on average, 100 ml of human adipose tissue yields about 1 x 10(6) stem cells. Studies conducted in porcine AMI models have shown a significant LV functional improvement, with no report of any potentially fatal arrhythmias. The APOLLO trial, a prospective, double blind, randomized, placebo-controlled trial currently in the recruiting phase, is a "first-in-man" study that explores the safety and feasibility of ADSC transplantation in patients with acute MI.

Adipose tissue-derived stem cells: the friendly side of a classic cardiovascular foe

Recently, the existence of a population of stem cells located in the adipose tissue has been observed. Adipose-derived stem cells are able to differentiate into multiple cell lineages including cardiac myocytes. Hence, adipose-derived cells are emerging as a new source of adult stem cells for cardiovascular repair. In this review, we discuss the basic principles of adipose-derived stem cells (types and characteristics, obtention processes, immunophenotypic characterization, and cell potency), the initial experimental studies, and the currently ongoing clinical trials.

Sphincter contractility after muscle-derived stem cells autograft into the cryoinjured anal sphincters of rats

PURPOSE

This study was designed to determine whether the injection of muscle-derived stem cells into the anal sphincter can improve functional properties in a fecal incontinence rat model.

METHODS

Cryoinjured rats were utilized as a fecal incontinence model. The gastrocnemius muscles of normal three-week-old female Sprague-Dawley rats were used for the purification of the muscle-derived stem cells. The experimental group was divided into three subgroups: normal control; cryoinjured; and muscle-derived stem cells (3 x 10(6) cells) injection group of cryoinjured rats. All groups were subsequently employed in contractility experiments using muscle strips from the anal sphincter, one week after preparation.

RESULTS

Contractility in the cryoinjured group was significantly lower than in the control after treatment with acetylcholine and KCl. In the muscle-derived stem cells injection group, contraction amplitude was higher than in the cryoinjured group but not significantly (20.5 +/- 21.3 vs. 17.3 +/- 3.4 g per gram tissue, with acetylcholine (10(-4) mol/l); 31 +/- 14.2 vs. 18.4 +/- 7.9 g per gram tissue, with KCl (10(-4) mol/l)). PKH-26-labeled transplanted cells were detected in all of the grafted sphincters. Differentiated muscle masses stained positively for alpha smooth muscle actin and myosin heavy chain at the muscle-derived stem cells injection sites.

CONCLUSIONS

This is the first study reporting that autologous muscle-derived stem cell grafts may be a tool for improving anal sphincter function.

Review article: Stem cell transplantation for the treatment of gastrointestinal diseases--current applications and future perspectives

BACKGROUND

Haematopoietic stem cell transplantation (HSCT) can be used to cure or ameliorate a variety of non-malignant diseases. These range from inherent defects of haematopoiesis, through metabolic diseases, to severe autoimmune diseases. The rationale for this strategy is based on the concept of immunoablation using high-dose chemotherapy, with subsequent regeneration of naïve T-lymphocytes derived from reinfused haematopoietic progenitor cells. Possibly the use of SCT allows the administration of high-dose chemotherapy resulting in a prompt remission in these therapy-refractory patients.

AIM

This review highlights the major scientific developments and defines the areas of successful use of HSCT in gastrointestinal disorders and gives a perspective on possible future applications.

METHODS

A search in the Medline has been conducted and all relevant published data were analysed.

RESULTS

HSCT has been proved successful in treating refractory Crohn's disease. A selected group of refractory coeliac patients having a high risk of developing enteropathy associated T-cell lymphoma has been recently treated with promising results. In cryptogenic cirrhosis, basic research and unpublished data concerning mesenchymal SCT are encouraging.

CONCLUSION

In refractory autoimmune gastrointestinal diseases, it seems that high-dose chemotherapy followed by HSCT is feasible and safe and might result in long-term improvement of disease activity.

Differences in stem and progenitor cell yield in different subcutaneous adipose tissue depots

BACKGROUND

Human adipose tissue has been shown to contain multipotent cells with properties similar to mesenchymal stromal cells. While there have been many studies of the biology of these cells, no study has yet evaluated issues associated with tissue harvest.

METHODS

Adipose tissue was obtained from the subcutaneous space of the abdomen and hips of 10 donors using both syringe and pump-assisted liposuction. Tissue was digested with collagenase and then assayed for the presence of different stem and progenitor cell types using clonogenic culture assays, including fibroblast colony-forming unit (CFU-F) and alkaline phosphatase-positive colony-forming unit (CFU-AP). Paired analysis of samples obtained from the same individual was used to compare harvest method and site.

RESULTS

Syringe suction provided significantly greater recovery of adipocytes and a non-significant trend towards improved recovery of cells in the adipocyte-depleted fraction. There was considerable donor-to-donor variation in stem cell recovery. However, paired analysis of tissue obtained from different subcutaneous sites in the same donor showed that tissue harvested from the hip yielded 2.3-fold more CFU-F/unit volume and a 7-fold higher frequency of CFU-AP than that obtained from the abdomen. These differences were statistically significant.

DISCUSSION

Harvest site influences the stem and progenitor cell content of subcutaneous adipose tissue.

Urogenital complications of Crohn's disease

Urogenital complications in Crohn's disease is a very narrow, specific area for consideration. The most frequent conditions that fall under this rubric include fistulous disease involving the genitourinary tract, nephrolithiasis, intrinsic renal diseases associated with Crohn's disease, and considerations in those who have had surgical procedures that alter normal pelvic anatomy. Fistulas involving the ureters, urinary bladder, and vagina are discussed. Nephrolithiasis is commonly in the form of calcium oxalate and uric acid, and is a well-known complication of Crohn's disease secondary to multiple mechanisms. Intrinsic renal disease is relatively rare and includes interstitial nephritis, amyloidosis, IgA nephropathy, and obstructive uropathy. Women who have undergone ileopouch anal anastomosis procedures are at risk for sexual dysfunction, dyspareunia, and decreased fecundity.

Structural fat grafting: more than a permanent filler

Grafted fat has many attributes of an ideal filler, but the results, like those of any procedure, are technique dependent. Fat grafting remains shrouded in the stigma of variable results experienced by most plastic surgeons when they first graft fat. However, many who originally reported failure eventually report success after altering their methods of harvesting, refinement, and placement. Many surgeons have refined their techniques to obtain long-term survival and volume replacement with grafted fat. They have observed that transplanted fat not only adjusts facial and body proportion but also improves surrounding tissues into which the fat is placed. They have noted not only the improvement in the quality of aging skin and scars but also a remarkable improvement in conditions such as radiation damage, chronic ulceration, breast capsular contracture, and damaged vocal cords. The mechanism of fat graft survival is not clear, and the role of adipose-derived stem cells and preadipocytes in fat survival remains to be determined. Early research has indicated the possible involvement of more undifferentiated cells in some of the observed effects of fat grafting on surrounding tissues. Of particular interest is the research that has pointed to the use of stem cells to repair and even to become bone, cartilage, muscle, blood vessels, nerves, and skin. Further studies are essential to understand grafted fat tissue.

Defecation disorders: neuromuscular aspects and treatment

Chronic constipation and fecal incontinence affect 20% of the population and are more prevalent in women, the elderly, those of lower socioeconomic status, and nursing home residents. These disorders pose a significant economic burden and affect quality of life. During the past decade, significant strides have been made in the understanding and treatment of defecation disorders, which have led to real advances in the management of these disorders. These treatments include biofeedback therapy, tegaserod, and lubiprostone for chronic constipation.

Adipose-derived stem cells for the regeneration of damaged tissues

As the promise of stem cell-based therapies begins to be realised, and efforts to bring advances to the clinic mount, the source of these cells is increasingly important. The morbidity associated with harvesting stem cells from solid organs and the invasive nature of bone marrow biopsies may limit their practicality for wider clinical applications. An emerging body of literature suggests that adipose tissue may provide an abundant, readily accessible source of cells with similar potential to that described of other adult stem cells. This review will address advances in the use of adipose stem cells in fields as divergent as soft tissue reconstruction and cerebral infarction recovery. Numerous challenges will also be discussed; however, rapidly accumulating advances suggest that adipose stem cells may be as effective as they are abundant.

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Fat tissue: an underappreciated source of stem cells for biotechnology

Adipose tissue can be harvested in large amounts with minimal morbidity. It contains numerous cells types, including adipocytes, preadipocytes, vascular endothelial cells and vascular smooth muscle cells; it also contains cells that have the ability to differentiate into several lineages, such as fat, bone, cartilage, skeletal, smooth, and cardiac muscle, endothelium, hematopoietic cells, hepatocytes and neuronal cells. Cloning studies have shown that some adipose-derived stem cells (ADSCs) have multilineage differentiation potential. ADSCs are also capable of expressing multiple growth factors, including vascular endothelial growth factor and hepatocyte growth factor. Early, uncontrolled, non-randomized clinical research, applying fresh adipose-derived cells into a cranial defect or undifferentiated ADSCs into fistulas in Crohn's disease, has shown healing and an absence of side effects. The combination of these properties, and the large quantity of cells that can be obtained from fat, suggests that this tissue will be a useful tool in biotechnology.

Medicina regenerativa con células madre adultas

The present state of clinical regenerative medicine with adult stem cells in the cardiology, digestive, corneal and neurological fields are reviewed. From the cardiology point of view, there is clinical experience with bone marrow stem cells and peripheral blood cells and with skeletal myoblasts. At present, the adult stem cells (bone marrow hematopoietic or mesenchymal) constitute the best option for the regeneration of heart tissue, the clinical studies showing favorable results without ethical or safety problems. Most of the studies with skeletal myoblasts have also been demonstrated to significantly contribute to improve heart function, above all, the systolic one. However they have the disadvantage that has not been totally clarified that they induce malignant ventricular arrhythmias. In either case, the clinical studies are in the initial phase and new studies, above all randomized, are necessary. In the digestive field, there is the pioneer experience of the Hospital La Paz on the use of stem cells from abdominal fat in the treatment of fistulous condition of patients with Crohn's disease. In ophthalmology, the limbal corneal transplant is a recognized practice, using cells from the contralateral eye when the damage is in a single eye and cells from a donor when the damage is bilateral. Finally, in the neurological field, different zones of the adult mammal brain where there are stem cells have been identified: the hippocampus, subventricular zone, olfactory bulb and periependymal zone of the spinal cord. On the other hand, neurons may be obtained from adult stem cells from other tissues, such as the bone marrow or adipose tissue, which means a practically unendable source of neural precursors, either by direct implant after their selection or after their in vitro culture. However, most of the experimentation is animal up to now, clinical trails on safety in amyotrophic lateral sclerosis are now being initiated.

Functional studies of mesenchymal stem cells derived from adult human adipose tissue

Recent evidence suggests that cells with the properties of human mesenchymal stem cells (hMSCs) can be derived from adult peripheral tissues, including adipose tissue, muscle and dermis. We isolated hMSCs from the stromal-vascular portion of subcutaneous adipose tissue from seven adult subjects. These cells could be readily differentiated into cells of the chondrocyte, osteocyte and adipocyte lineage demonstrating their multipotency. We studied the functional properties of hMSCs-derived adipocytes and compared them with adipocytes differentiated from hMSCs obtained from bone marrow (BM-hMSC). The two cell types displayed similar lipolytic capacity upon stimulation with catecholamines, including a pronounced antilipolytic effect mediated through alpha2A-adrenoceptors, a typical trait in human but not rodent fat cells. Furthermore, both cell types secreted the fat cell-specific factors leptin and adiponectin in comparable amounts per time unit. The fat tissue-derived hMSCs retained their differentiation capacity up to at least fifteen passages. We conclude that hMSCs derived from adult human adipose tissue can be differentiated into fully functional adipocytes with a similar, if not identical, phenotype as that observed in cells derived from BM-hMSCs. Human adipose-tissue-derived MSCs could therefore constitute an efficient and easily obtainable renewable cellular source for studies of adipocyte biology.

A phase I clinical trial of the treatment of Crohn's fistula by adipose mesenchymal stem cell transplantation

PURPOSE

The effective management of fistulas in patients with Crohn's disease presents an extremely challenging problem. Mesenchymal adult stem cells extracted from certain tissues, such as adipose tissue, can differentiate into various cell types. Therefore, we have tried to use such cells to stimulate healing of Crohn's fistulas.

METHODS

We designed a prospective Phase I clinical trial, involving five patients with Crohn's disease, to test the feasibility and safety of autologous stem cells transplantation in the treatment of fistulas. We also studied the expression of various cell markers and the growth rates of the lipoaspirate-derived cells that were used for transplantation.

RESULTS

One patient was excluded because of bacterial contamination of cultured cells. We inoculated nine fistulas in four patients with autologous adipose tissue-derived stem cells at Passage 3 or earlier. Eight inoculated fistulas were followed weekly for at least eight weeks. In six fistulas, the external opening was covered with epithelium at the end of Week 8, and, thus, these fistulas were considered healed (75 percent). In the other two fistulas, there was only incomplete closure of the external opening, with a decrease in output flow (not healed; 25 percent). No adverse effects were observed in any patient at the end of the follow-up period (minimum follow-up,12 months; maximum follow-up, 30 months; follow-up average, 22 months).

CONCLUSIONS

To our knowledge, this is the first report of a clinical trial of cell therapy using autologous stem cells obtained from a lipoaspirate. Our results indicate that our protocol is feasible and safe for the treatment of fistulas in Crohn's disease. The number of patients included and the uncontrolled nature of Phase I clinical trials do not allow demonstration of the effectiveness of the treatment. However, the results of the present study encourage to perform further studies in Phase II.

Management of Perianal Crohn's Disease

Perianal manifestations of Crohn's disease usually coexist with active inflammation of other primary sites of the disease. Although treatment of active proximal disease may sometimes alleviate perianal symptoms, it is reasonable to separately treat symptomatic perianal disease. The diversity of perianal manifestations in Crohn's disease mandates a tailored, individualized approach in every case. Medical therapy is the best treatment option for hemorrhoids and anal fissures. The medical management of patients with perianal Crohn's disease includes the use of systemic antibiotics, immunosuppressive agents, and infliximab. Infliximab is now recognized as a very efficacious agent for treating fistulizing Crohn's disease, including perianal fistulae. It may also reduce the need for surgical intervention in specific cases. Abscesses and fistulae are treated by control of sepsis, resolution of inflammation and optimal preservation of continence, and quality of life. Abscesses require surgical drainage that may need to be prolonged to achieve complete healing. Fistulae may be treated medically, especially in cases of concurrent proctitis. Refractory fistulae may require surgical treatment including an occasional need for fecal diversion or proctectomy. The role of new treatment options such as natalizumab and CDP571 is evolving and requires further investigation.

Advances in medical therapy for Crohn's disease

Therapeutic research in Crohn's disease has been intensified in recent years. This has led to many novel approaches and insights into the mechanism of action of "classic" drugs. Antibiotics remain valuable but do not offer benefit when used in addition to corticosteroids. Immunomodulators remain the cornerstone for maintenance therapy, although certain corticosteroid-dependent patients can be switched to maintenance therapy with topical steroids. Azathioprine and 6-mercaptopurine remain efficient beyond 4 years in patients with relapses and elevated C-reactive protein in spite of this therapy. Infliximab has shown efficiency in maintenance of active and fistulizing Crohn's disease. In addition, "automatic reinfusion" was found to be superior to "on-demand" treatment. Infusion reactions and loss of response, most often caused by antibodies against infliximab, can be prevented with immunomodulators and corticosteroid infusions before dosing. Such alternative anti-tumor necrosis factor agents as adalimumab or CDP-870 may be less immunogenic. Other biologic agents, such as the anti-integrin monoclonal antibody natalizumab, were shown to be effective in maintaining remission and somewhat less so in induction of remission. Finally, much attention is being paid to alteration of the luminal flora with probiotics and helminth ova. Extracorporeal apheresis and even stem cell transplantation were found to be effective in isolated patients, but these therapies warrant further prospective and controlled investigation.

Bone and fat: old questions, new insights

Until recently, adipose tissue was considered to serve only as a triglyceride reservoir and was relegated to a passive endocrine role. With the discovery of leptin and other adipokines, adipose tissue is now recognized as an active participant in systemic metabolism. This review focuses on the complex relationship existing between adipose tissue and bone metabolism and differentiation. It explores the paradigms that have shaped the past decade's research and what these findings forecast for the future. Particular attention is given to the multipotent adult stem cell populations that reside within bone and fat. These adult stem cells have critical importance to the emerging field of tissue engineering and regenerative medicine.