Papers by Peter Alexander
Journal of Experimental Orthopaedics
Purpose Development and validation of an animal model of labral healing would facilitate translat... more Purpose Development and validation of an animal model of labral healing would facilitate translation of novel surgical and biological strategies to improve glenolabral healing. The purpose of this study was to characterize the anatomic and histological properties of the shoulder labrum in rat, rabbit, dog, pig, goat, and humans. Given the demonstrated similarities in size and structural morphology in other joints, it was hypothesized that the goat glenoid with surrounding capsulolabral complex would most closely resemble that of humans in terms of dimensions and structure, as observed grossly and histologically. Methods Cadaveric glenohumeral joints from rats (n = 8), New Zealand white rabbits (n = 13), Mongrel dogs (n = 9), Spanish goats (n = 10), Yorkshire pigs (n = 10), and humans (n = 9) were freshly harvested. Photographs were taken of the glenoid with its surrounding capsulolabral complex. Linear dimensions of the glenoid articular surface were measured. It was determined wher...
Biology
Osteoarthritis (OA) is a chronic degenerative joint disease that causes pain, physical disability... more Osteoarthritis (OA) is a chronic degenerative joint disease that causes pain, physical disability, and life quality impairment. The pathophysiology of OA remains largely unclear, and currently no FDA-approved disease-modifying OA drugs (DMOADs) are available. As has been acknowledged, aging is the primary independent risk factor for OA, but the mechanisms underlying such a connection are not fully understood. In this review, we first revisit the changes in OA chondrocytes from the perspective of cellular hallmarks of aging. It is concluded that OA chondrocytes share many alterations similar to cellular aging. Next, based on the findings from studies on other cell types and diseases, we propose methods that can potentially reverse osteoarthritic phenotype of chondrocytes back to a healthier state. Lastly, current challenges and future perspectives are summarized.
Supplemental material, DS_10.1177_0363546518782973 for In Vitro Repair of Meniscal Radial Tear Wi... more Supplemental material, DS_10.1177_0363546518782973 for In Vitro Repair of Meniscal Radial Tear With Hydrogels Seeded With Adipose Stem Cells and TGF-β3 by Hiroshi Sasaki, Benjamin B. Rothrauff, Peter G. Alexander, Hang Lin, Riccardo Gottardi, Freddie H. Fu and Rocky S. Tuan in The American Journal of Sports Medicine
Supplemental material, DS_10.1177_0363546519880468 for Point-of-Care Procedure for Enhancement of... more Supplemental material, DS_10.1177_0363546519880468 for Point-of-Care Procedure for Enhancement of Meniscal Healing in a Goat Model Utilizing Infrapatellar Fat Pad–Derived Stromal Vascular Fraction Cells Seeded in Photocrosslinkable Hydrogel by Benjamin B. Rothrauff, Hiroshi Sasaki, Shinsuke Kihara, Kalon J. Overholt, Riccardo Gottardi, Hang Lin, Freddie H. Fu, Rocky S. Tuan and Peter G. Alexander in The American Journal of Sports Medicine
The aim of the present study was to investigate the role of Notch signaling in the pathogenesis o... more The aim of the present study was to investigate the role of Notch signaling in the pathogenesis of osteoarthritis (OA). OA is a slowly progressive degenerative disease characterized by gradual loss of articular cartilage accompanied by aberrant repair, resulting in remodeling of the subchondral bone and osteophyte formation. Alsalameh, et al. and Dowthwaite, et al. identified mutlipotential mesenchymal progenitor cells in adult human articular cartilage, specifically on the surface of the cartilage (2003 and 2004). The Notch signaling pathway is a highly conserved signaling system that plays a critical role in cell proliferation, differentiation, and apoptosis in the context of stem cell differentiation. Thus, aberrant regulation of Notch signaling may adversely affect the chondrogenesis of articular cartilage mesenchymal stem cells (MSCs) in diseased tissue. Materials and Methods: Tissue: Normal human articular cartilage was isolated from tissue purchased from the National Disease Research Interchange, OA articular cartilage was obtained from patients (age 53-79 years) undergoing elective total knee arthroplasty, and bone marrow aspirate was obtained according to an approved IRB protocol. Human cell Isolation and Cell Culture: Cartilage was digested with 1mg/ml collagenase II in a volume of 10 ml/g wet weight cartilage in serum-free medium overnight at 37oC under agitation. The chondrocyte (hCh) suspension was filtered, washed, and plated in DMEM containing 10% FBS and antibiotic-antimycotic solutions. Cells were allowed to adhere, spread and proliferate for 7-10 days. Normal and OA hChs were used for experiments between P1 and P2. Bone marrow aspirate was washed with DMEM and pelleted at 1000 g's for 5 min. repeating twice and resuspending in DMEM. Cells were plated DMEM containing 10% FBS and antibiotic-antimycotic solutions. 24 h later, the cells were washed. The remaining adherent cells (MSCs) were then proliferated. RNA processing: Total RNA was isolated using a Qiagen RNeasy kit. cDNA was generated using Invitrogen Superscript First-Strand synthesis. A Bio-Rad iCycler iQ qRT-PCR system was utilized to analyze transcript levels of Notch components in OA (Mankin score of 6) and normal tissue and monolayer hChs and MSCs. GeNorm 3.5 was used to create normalization factors for comparing normal cartilage, OA cartilage, monolayer MSCs, and monolayer hChs utilitzing GAPDH, β-Actin, HMBS, RPL13A, SDHA, and UBC as housekeeping genes.. Differentiation: MSCs and hChs were cultured in high-density pellets in serum-free chondrogenic media. Pellets were cultured in the presence of 0.1, 1, and 10 ng/mL IL-1beta to mimic osteoarthritic conditions for 21 days. Histo-and Immuno-chemistry: Histological staining was performed on primary tissue and harvested pellets with H&E, alcian blue (pH 1.0), alizarin red, fast green, and safrinin O. Cartilage was evaluated for morphology, cellular abnormality, matrix staining, and tidemark integrities using the Mankin scale (Mankin 1971). Sections were pre-digested with hyaluronidase in 10 mM Tris-HCl, pH 7.5, for 30 min at 37oC, then incubated at room temperature with the indicated antibodies in Tris buffered saline (pH 7.4) containing 0.1% BSA. Specific antibodies to Notch components were obtained from Molecular Probes. Immunostaining was detected by using Vector kits. Results: The expression of Notch1, Notch2, Jagged1, and Delta1 is down regulated in OA compared to normal cartilage 200-, 12-, 34-, and 30-fold (Fig 1). Notch1 expression is absent in monolayer hChs, highly expressed in normal cartilage, and similarly expressed in monolayer MSCs and OA cartilage. During in vitro
Biology, 2020
As the most common chronic degenerative joint disease, osteoarthritis (OA) is the leading cause o... more As the most common chronic degenerative joint disease, osteoarthritis (OA) is the leading cause of pain and physical disability, affecting millions of people worldwide. Mainly characterized by articular cartilage degradation, osteophyte formation, subchondral bone remodeling, and synovial inflammation, OA is a heterogeneous disease that impacts all component tissues of the articular joint organ. Pathological changes, and thus symptoms, vary from person to person, underscoring the critical need of personalized therapies. However, there has only been limited progress towards the prevention and treatment of OA, and there are no approved effective disease-modifying osteoarthritis drugs (DMOADs). Conventional treatments, including non-steroidal anti-inflammatory drugs (NSAIDs) and physical therapy, are still the major remedies to manage the symptoms until the need for total joint replacement. In this review, we provide an update of the known OA risk factors and relevant mechanisms of act...
The generation of engineered models of the osteochondral complex to study its pathologies and dev... more The generation of engineered models of the osteochondral complex to study its pathologies and develop possible treatments is hindered by the distinctly different properties of articular cartilage and subchondral bone, with the latter characterized by vascularization. In vitro models of the osteochondral complex have been mainly engineered as biphasic constructs containing just cartilage and bone cells, a condition very dissimilar from the in vivo environment. The different cellular components of the osteochondral complex are governed by interacting biochemical signaling; hence, to study the crosstalk among chondrocytes, osteoblasts, and endothelial cells, we have developed a novel triphasic model of the osteochondral tissue interface. Wet-spun poly(ε-caprolactone) (PCL) and PCL/hydroxyapatite (HA) scaffolds in combination with a methacrylated gelatin (gelMA) hydrogel were used as the polymeric backbone of the constructs. The scaffold components were engineered with human bone marrow...
Bone & Joint Research, 2020
Aims Dystrophic calcification (DC) is the abnormal appearance of calcified deposits in degenerati... more Aims Dystrophic calcification (DC) is the abnormal appearance of calcified deposits in degenerating tissue, often associated with injury. Extensive DC can lead to heterotopic ossification (HO), a pathological condition of ectopic bone formation. The highest rate of HO was found in combat-related blast injuries, a polytrauma condition with severe muscle injury. It has been noted that the incidence of HO significantly increased in the residual limbs of combat-injured patients if the final amputation was performed within the zone of injury compared to that which was proximal to the zone of injury. While aggressive limb salvage strategies may maximize the function of the residual limb, they may increase the possibility of retaining non-viable muscle tissue inside the body. In this study, we hypothesized that residual dead muscle tissue at the zone of injury could promote HO formation. Methods We tested the hypothesis by investigating the cellular and molecular consequences of implanting...
Frontiers in Bioengineering and Biotechnology, 2019
Osteoarthritis (OA) is a chronic disease mainly characterized by degenerative changes in cartilag... more Osteoarthritis (OA) is a chronic disease mainly characterized by degenerative changes in cartilage, but other joint elements such as bone are also affected. To date, there are no disease-modifying OA drugs (DMOADs), owing in part to a deficiency of current models in simulating OA pathologies and etiologies in humans. In this study, we aimed to develop microphysiological osteochondral (OC) tissue chips derived from human induced pluripotent stem cells (iPSCs) to model the pathologies of OA. We first induced iPSCs into mesenchymal progenitor cells (iMPCs) and optimized the chondro-and osteo-inductive conditions for iMPCs. Then iMPCs were encapsulated into photocrosslinked gelatin scaffolds and cultured within a dual-flow bioreactor, in which the top stream was chondrogenic medium and the bottom stream was osteogenic medium. After 28 days of differentiation, OC tissue chips were successfully generated and phenotypes were confirmed by real time RT-PCR and histology. To create an OA model, interleukin-1β (IL-1β) was used to challenge the cartilage component for 7 days. While under control conditions, the bone tissue promoted chondrogenesis and suppressed chondrocyte terminal differentiation of the overlying chondral tissue. Under conditions modeling OA, the bone tissue accelerated the degradation of chondral tissue which is likely via the production of catabolic and inflammatory cytokines. These findings suggest active functional crosstalk between the bone and cartilage tissue components in the OC tissue chip under both normal and pathologic conditions. Finally, a selective COX-2 inhibitor commonly prescribed drug for OA, Celecoxib, was shown to downregulate the expression of catabolic and proinflammatory cytokines in the OA model, demonstrating the utility of the OC tissue chip model for drug screening. In summary, the iPSC-derived OC tissue chip developed in this study represents a high-throughput platform applicable for modeling OA and for the screening and testing of candidate DMOADs.
The American Journal of Sports Medicine, 2019
Background: Large radial tears of the meniscus involving the avascular region can compromise meni... more Background: Large radial tears of the meniscus involving the avascular region can compromise meniscal function and result in poor healing and subsequent osteochondral degeneration. Augmentation of surgical repairs with adipose-derived stromal vascular fraction (SVF), which contains mesenchymal stromal cells, may improve meniscal healing and preserve function (ie, chondroprotection). Purposes: (1) To develop a goat model of a radial meniscal tear with resulting osteoarthritis and (2) to explore the efficacy of a 1-step procedure utilizing infrapatellar fat pad–derived SVF cells seeded in a photocrosslinkable hydrogel to enhance meniscal healing and mitigate osteochondral degeneration. Study Design: Controlled laboratory study. Methods: A full-thickness radial tear spanning 90% of the medial meniscal width was made at the junction of the anterior and middle bodies of the goat stifle joint. Tears received 1 of 3 interventions (n = 4 per group): untreated, repair, or repair augmented wi...
BMC Musculoskeletal Disorders, 2019
Background: The purpose of the study was to evaluate whether tranexamic acid (TXA) administration... more Background: The purpose of the study was to evaluate whether tranexamic acid (TXA) administration could reduce blood loss and transfusion risk after simultaneous bilateral total knee arthroplasty (SBTKA). Methods: As a multicenter retrospective study, a total of 575 patients were assigned into three groups on the basis of TXA usage, including intravenous (IV) group (1 g IV TXA 5-10 min prior to the incision), combined group (1 g IV TXA combined with intra-articular injection of 1 g TXA prior to the closure every knee) and control group (no TXA use). The primary outcomes were total blood loss (TBL). The secondary outcomes were maximum hemoglobin (Hb) and hematocrit (Hct) drop, transfusion rate, drain volume, length of stay, hospitalization expenses and the incidence of complications. Results: The mean TBL in control group (1685.0 ± 571.4 mL) were higher than that in IV group (1061.1 ± 689.6 mL, p = 0.006 and combined group (988.3 ± 559.3 mL, p = 0.003). The maximum Hb and Hct drop in combined group (28.5 ± 13.4 g/L, p = 0.016; 0.074 ± 0.053, p < 0.001) and IV group (28.8 ± 14.5 g/L, p = 0.025; 0.082 ± 0.056, p = 0.001) were lower than those in control group (33.4 ± 14.0; 0.131 ± 0.049). But the difference between IV and combined groups was not significant. The similar trend was detected on drain volume, length of stay and hospitalization expenses. The incidence of complications did not differ significantly among the three groups (p > 0.05). Conclusions: The study indicates that TXA could reduce blood loss with no apparent increase in the incidence of complications during SBTKA.
Osteoarthritis and Cartilage, 2017
Principles of Tissue Engineering, 2014
Abstract Mesenchymal stem cells (MSCs) found in adult tissues function as progenitor cells that c... more Abstract Mesenchymal stem cells (MSCs) found in adult tissues function as progenitor cells that can proliferate and differentiate into various mesenchymal cell lineages, including those that are the building blocks of musculoskeletal system. Due to their ease of isolation, extensive proliferation capacity, and multilineage differentiation potential, MSCs are considered the cell type of choice for musculoskeletal tissue engineering. This chapter will first survey current knowledge of MSC biology that serves as the scientific foundation to guide approaches in musculoskeletal tissue engineering. Relevant information regarding MSC tissue origin, isolation, and in vitro culture, and factors controlling their proliferation as well as multipotential differentiation will be reviewed. In addition, recent recognition of the immunosuppressive and immunomodulatory properties of MSCs will be discussed, as this is critical for the safe usage of MSCs in allogeneic transplantation, which is often the case with tissue-engineered products. In the second part, we survey the use of MSCs in the engineering of musculoskeletal tissues, including cartilage, bone, tendon, and osteochondral constructs. We review the biological processes that regulate multilineage differentiation of MSCs and the factors that regulate the ultimate outcome of engineered tissue replacement, with particular focus on cartilage and bone. Current approaches to optimizing the three critical elements of successful tissue engineering, namely, cells, scaffolds, and environment, are discussed, with emphasis on the promotion of cartilage tissue engineering and restoration. While MSCs hold great potential for musculoskeletal systems, there are challenges, from a better understanding of their biology, to the application of such information to optimize tissue neogenesis and the development of functional scaffolds for tissue engineering.
Stem Cell Research & Therapy, 2013
Osteoarthritis is a disease of the osteochondral junction Osteoarthritis (OA) is a chronic degene... more Osteoarthritis is a disease of the osteochondral junction Osteoarthritis (OA) is a chronic degenerative disease of the articular joint that involves cartilage, synovium, ligaments, bone, meniscus, tendon, and periarticular muscle [1]. Cartilage destruction is one of the common characteristics of OA progression and results in malfunction of the aff ected joint. Normal articular cartilage is comprised of large amounts of extracellular matrix (mainly collagen type II), produced and maintained by chondrocytes, the sole cell type in the cartilage. During disease progression, net loss of cartilage matrix results from an imbalance between cartilage matrix degradation and synthesis by chondrocytes in the cartilage [2-4]. Due to absence of vascularization in the articular cartilage, the capacity for self-repair in cartilage is limited, and currently there is no eff ective therapy treating OA except for relieving the symptoms of the diseases until the joints need to be replaced by surgery. OA involves more than simply degeneration of the articular cartilage-OA is in fact a disease of the osteochondral tissue complex. Th e osteochondral junction is highly structured [5-7]; the uppermost superfi cial zone is characterized by elongated chondrocytes with collagen fi brils aligning parallel to the articular surface. In the middle/intermediate zone, rounded chondrocytes and collagen fi brils are less organized relative to the surface. In the deep zone, vertical columns of chondrocytes and Abstract Osteoarthritis (OA), the most prevalent form of arthritis, aff ects up to 15% of the adult population and is principally characterized by degeneration of the articular cartilage component of the joint, often with accompanying subchondral bone lesions. Understanding the mechanisms underlying the pathogenesis of OA is important for the rational development of disease-modifying OA drugs. While most studies on OA have focused on the investigation of either the cartilage or the bone component of the articular joint, the osteochondral complex represents a more physiologically relevant target because the disease ultimately is a disorder of osteochondral integrity and function. In our current investigation, we are constructing an in vitro three-dimensional microsystem that models the structure and biology of the osteochondral complex of the articular joint. Osteogenic and chondrogenic tissue components are produced using adult human mesenchymal stem cells derived from bone marrow and adipose seeded within biomaterial scaff olds photostereolithographically fabricated with defi ned internal architecture. A three-dimensionalprinted, perfusion-ready container platform with dimensions to fi t into a 96-well culture plate format is designed to house and maintain the osteochondral microsystem that has the following features: an anatomic cartilage/bone biphasic structure with a functional interface; all tissue components derived from a single adult mesenchymal stem cell source to eliminate possible age/tissue-type incompatibility; individual compartments to constitute separate microenvironment for the synovial and osseous components; accessible individual compartments that may be controlled and regulated via the introduction of bioactive agents or candidate eff ector cells, and tissue/medium sampling and compositional assays; and compatibility with the application of mechanical load and perturbation. The consequences of mechanical injury, exposure to infl ammatory cytokines, and compromised bone quality on degenerative changes in the cartilage component are examined in the osteochondral microsystem as a fi rst step towards its eventual application as an improved and high-throughput in vitro model for prediction of effi cacy, safety, bioavailability, and toxicology outcomes for candidate disease-modifying OA drugs.
Osteoarthritis and Cartilage, 2014
Molecular Pharmaceutics, 2014
Osteoarthritis (OA) is a chronic degenerative disease of the articular joint that involves both b... more Osteoarthritis (OA) is a chronic degenerative disease of the articular joint that involves both bone and cartilage degenerative changes. An engineered osteochondral tissue within physiological conditions will be of significant utility in understanding the pathogenesis of OA and testing the efficacy of potential disease-modifying OA drugs (DMOADs). In this study, a multichamber bioreactor was fabricated and fitted into a microfluidic base. When the osteochondral construct is inserted, two chambers are formed on either side of the construct (top, chondral; bottom, osseous) that is supplied by different medium streams. These medium conduits are critical to create tissue-specific microenvironments in which chondral and osseous tissues will develop and mature. Human bone marrow stem cell (hBMSCs)-derived constructs were fabricated in situ and cultured within the bioreactor and induced to undergo spatially defined chondrogenic and osteogenic differentiation for 4 weeks in tissue-specific media. We observed tissue specific gene expression and matrix production as well as a basophilic interface suggesting a developing tidemark. Introduction of interleukin-1β (IL-1β) to either the chondral or osseous medium stream induced stronger degradative responses locally as well as in the opposing tissue type. For example, IL-1β treatment of the osseous compartment resulted in a strong catabolic response in the chondral layer as indicated by increased matrix metalloproteinase (MMP) expression and activity, and tissue-specific gene expression. This induction was greater than that seen with IL-1β application to the chondral component directly, indicative of active biochemical communication between the two tissue layers and supporting the osteochondral nature of OA. The microtissue culture system developed here offers novel capabilities for investigating the physiology of osteochondral tissue and pathogenic mechanisms of OA and serving as a highthroughput platform to test potential DMOADS.
Arthritis Research & Therapy, 2012
Stem cell research & therapy, Jan 13, 2017
Adult mesenchymal stem cells (MSCs) have been shown to increase nerve regeneration in animal mode... more Adult mesenchymal stem cells (MSCs) have been shown to increase nerve regeneration in animal models of nerve injury. Traumatized muscle-derived multipotent progenitor cells (MPCs) share important characteristics with MSCs and are isolated from severely damaged muscle tissue following surgical debridement. Previous investigations have shown that MPCs may be induced to increase production of several neurotrophic factors, suggesting the possible utility of autologous MPCs in peripheral nerve regeneration following injury. Recent findings have also shown that components of the vascular niche, including endothelial cells (ECs) and vascular endothelial growth factor (VEGF)-A, regulate neural progenitor cells and sensory neurons. In this study, we have investigated the neuroinductive activities of MPCs, particularly MPC-produced VEGF-A, in the context of an aligned, neuroconductive nerve guide conduit and the endothelial component of the vascular system. Embryonic dorsal root ganglia (DRG)...
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Papers by Peter Alexander