Objective: The differentiation of mesenchymal stem cells (MSCs) into chondrocytes provides an attractive basis for the repair and regeneration of articular cartilage. Under clinical conditions, chondrogenesis will often need to occur in the presence of mediators of inflammation produced in response to injury or disease. The purpose of this study was to examine the effects of 2 important inflammatory cytokines, interleukin‐1β (IL‐1β) and tumor necrosis factor α (TNFα), on the chondrogenic behavior of human MSCs.Methods: Aggregate cultures of MSCs recovered from the femoral intermedullary canal were used. Chondrogenesis was assessed by the expression of relevant transcripts by quantitative reverse transcription–polymerase chain reaction analysis and examination of aggregates by histologic and immunohistochemical analyses. The possible involvement of NF‐κB in mediating the effects of IL‐1β was examined by delivering a luciferase reporter construct and a dominant‐negative inhibitor of NF‐κB (suppressor‐repressor form of IκB [srIκB]) with adenovirus vectors.Results: Both IL‐1β and TNFα inhibited chondrogenesis in a dose‐dependent manner. This was associated with a marked activation of NF‐κB. Delivery of srIκB abrogated the activation of NF‐κB and rescued the chondrogenic response. Although expression of type X collagen followed this pattern, other markers of hypertrophic differentiation responded differently. Matrix metalloproteinase 13 was induced by IL‐1β in a NF‐κB–dependent manner. Alkaline phosphatase activity, in contrast, was inhibited by IL‐1β regardless of srIκB delivery.Conclusion: Cell‐based repair of lesions in articular cartilage will be compromised in inflamed joints. Strategies for enabling repair under these conditions include the use of specific antagonists of individual pyrogens, such as IL‐1β and TNFα, or the targeting of important intracellular mediators, such as NF‐κB.

Intra‐articular (i.a.) drug delivery for local treatment of osteoarthritis remains inadequate due to rapid clearance by the vasculature or lymphatics. Local therapy targeting articular cartilage is further complicated by its dense meshwork of collagen and negatively charged proteoglycans, which can prevent even nano‐sized solutes from entering. In a previous in vitro study, we showed that Avidin, due to its size (7 nm diameter) and high positive charge (pI 10.5), penetrated the full thickness of bovine cartilage and was retained for 15 days. With the goal of using Avidin as a nano‐carrier for cartilage drug delivery, we investigated its transport properties within rat knee joints. Avidin penetrated the full thickness of articular cartilage within 6 h, with a half‐life of 29 h, and stayed inside the joint for 7 days after i.a. injection. The highest concentration of Avidin was found in cartilage, the least in patellar tendon and none in the femoral bone; in contrast, negligible Neutravidin (neutral counterpart of Avidin) was present in cartilage after 24 h. A positive correlation between tissue sGAG content and Avidin uptake (R² = 0.83) confirmed the effects of electrostatic interactions. Avidin doses up to at least 1 µM did not affect bovine cartilage explant cell viability, matrix catabolism or biosynthesis. © 2014 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 32:1044–1051, 2014.

Facilitated endogenous repair is a novel approach to tissue engineering that avoids the ex vivo culture of autologous cells and the need for manufactured scaffolds, while minimizing the number and invasiveness of associated clinical procedures. The strategy relies on harnessing the intrinsic regenerative potential of endogenous tissues using molecular stimuli, such as gene transfer, to initiate reparative processes in situ. In the simplest example, direct percutaneous injection of an osteogenic vector is used to stimulate bone healing. If necessary, additional progenitor cells and space-filling scaffolds can be provided by autologous bone marrow, muscle, fat, and perhaps other tissues. These can be harvested, processed, and reimplanted by simple, expedited, intraoperative procedures. Examples of repair of experimental osseous and osteochondral lesions in laboratory animals are described. If successful, these strategies will provide methods for tissue regeneration that are not only effective but also inexpensive, safe, and clinically expeditious. Although orthopaedic examples are given here, the technology should be more generally applicable.

Intramedullary nailing preceded by canal reaming is the current standard of treatment for long‐bone fractures requiring stabilization. However, conventional reaming methods can elevate intramedullary temperature and pressure, potentially resulting in necrotic bone, systemic embolism, and pulmonary complications. To address this problem, a reamer irrigator aspirator (RIA) has been developed that combines irrigation and suction for reduced‐pressure reaming with temperature modulation. Osseous particles aspirated by the RIA can be recovered by filtration for use as an autograft, but the flow‐through is typically discarded. The purpose of this study was to assess whether this discarded filtrate has osteogenic properties that could be used to enhance the total repair potential of aspirate. RIA aspirate was collected from five patients (ages 71–78) undergoing hip hemiarthroplasty. Osseous particles were removed using an open‐pore filter, and the resulting filtrate (230 ± 200 mL) was processed by Ficoll‐gradient centrifugation to isolate mononuclear cells (6.2 ± 5.2 × 10⁶ cells/mL). The aqueous supernatant contained FGF‐2, IGF‐I, and latent TGF‐β1, but BMP‐2 was below the limit of detection. The cell fraction included culture plastic‐adherent, fibroblastic cells that displayed a surface marker profile indicative of mesenchymal stem cells and that could be induced along the osteogenic, adipogenic, and chondrogenic lineages in vitro. When compared to outgrowth cells from the culture of osseous particles, filtrate cells were more sensitive to seeding density during osteogenic culture but had similar capacity for chondrogenesis. These results suggest using RIA aspirate to develop improved, clinically expeditious, cost‐effective technologies for accelerating the healing of bone and other musculoskeletal tissues. © 2008 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 27:42–49, 2009

When ruptured, the anterior cruciate ligament (ACL) of the human knee has limited regenerative potential. However, the goal of this report was to show that the cells that migrate out of the human ACL constitute a rich population of progenitor cells and we hypothesize that they display mesenchymal stem cell (MSC) characteristics when compared with adherent cells derived from bone marrow or collagenase digests from ACL. We show that ACL outgrowth cells are adherent, fibroblastic cells with a surface immunophenotype strongly positive for cluster of differentiation (CD)29, CD44, CD49c, CD73, CD90, CD97, CD105, CD146, and CD166, weakly positive for CD106 and CD14, but negative for CD11c, CD31, CD34, CD40, CD45, CD53, CD74, CD133, CD144, and CD163. Staining for STRO-1 was seen by immunohistochemistry but not flow cytometry. Under suitable culture conditions, the ACL outgrowth-derived MSCs differentiated into chondrocytes, osteoblasts, and adipocytes and showed capacity to self-renew in an in vitro assay of ligamentogenesis. MSCs derived from collagenase digests of ACL tissue and human bone marrow were analyzed in parallel and displayed similar, but not identical, properties. In situ staining of the ACL suggests that the MSCs reside both aligned with the collagenous matrix of the ligament and adjacent to small blood vessels. We conclude that the cells that emigrate from damaged ACLs are MSCs and that they have the potential to provide the basis for a superior, biological repair of this ligament.