Relationship of polypharmacy to HIV RNA suppression in people aged ≥ 50 years living with HIV.

OBJECTIVES: People living with HIV (PLWH) aged ≥ 50 years face unique challenges regarding their medication therapies, especially antiretroviral therapy (ART). Use of ARTs, along with medications for comorbidities, may lead to adverse events, drug-drug interactions (DDIs) and poor adherence. The objective of this study was to identify the number of medications above which PLWH aged ≥ 50 years are less likely to be virally suppressed and to describe other associated patient-specific risk factors. METHODS: This was a cross-sectional study of PLWH aged ≥ 50 years, prescribed ART, and seen at least once in the Northwestern Infectious Disease Center between 1 June 2013 and 31 May 2015. Variables concerning medication use and comorbidities were collected. The primary outcome was the presence of an undetectable plasma HIV RNA level (viral load). RESULTS: Among the 621 included patients, there was a higher percentage taking ≤ 15 medications with an undetectable plasma HIV RNA (n = 453; 80.6%) vs. patients taking > 15 medications (n = 40; 67.8%; P = 0.03). Taking > 15 medications [odds ratio (OR) 0.49; 95% confidence interval (CI) 0.26-0.96], pulmonary disease (OR 0.54; 95% CI 0.3-0.97) and CD4 T-lymphocyte count < 200 cells/µL (OR 0.39; 95% CI 0.22-0.68) decreased the odds of having an undetectable plasma HIV RNA. CONCLUSIONS: PLWH taking > 15 medications were less likely to have an undetectable HIV RNA. Further studies are needed to evaluate the impact of overall medication economic burden on clinical outcomes among PLWH ≥ 50 years of age.

Comparison of micro-CT post-processing methods for evaluating the trabecular bone volume fraction in a rat ACL-transection model.

Trabecular bone volume fraction assessments are likely sensitive to the analysis method and selection of the region of interest. Currently, there are several methods for selecting the region of interest to analyze trabecular bone in animal models of post-traumatic osteoarthritis. The objective of this study was to compare three published methods for determining the trabecular bone volume fraction of the medial tibial epiphyses in ACL transected and contralateral ACL intact knees. Micro-computed tomography images of both knees were obtained five weeks post-operatively and evaluated using three methods: (1) the Whole Compartment Method that captured the entire medial compartment, (2) the centrally located Single Core Method, and (3) the Triplet Core Method that averaged focal locations in the anterior, central, and posterior regions. The Whole Compartment Method detected significant bone loss in the ACL transected knee compared to the ACL intact knee (p<0.001), with a loss of 15.2±3.9%. The Single Core and the Triplet Core Methods detected losses of 7.5±10.5% (p=0.061) and 14.1±13.7%(p=0.01), respectively. Details regarding segmentation methods are important for facilitating comparisons between studies, and for selecting methods to document trabecular bone changes and treatment outcomes. Based on these findings, the Whole Compartment Method is recommended, as it was least variable and more sensitive for detecting differences in the bone volume fraction in the medial compartment.

Improving the clinical efficiency of T2(*) mapping of ligament integrity.

Current MR methods use T2(*) relaxation time as a surrogate measure of ligament strength. Currently, a multi-echo voxel-wise least squares fit is the gold standard to create T2(*) maps; however, the post-processing is time-intensive and serves as a stopgap for clinical use. The study objective was to determine if an alternative method could improve post-processing time without sacrificing fidelity of T2(*) values for eventual translational use in the clinic. Using a 6 echo FLASH sequence, three different methods were used to determine intact posterior cruciate ligament (PCL) median T2(*) Two of these methods utilized a voxel-wise method to establish T2(*) maps: (1) a current "gold standard" method using a voxel-wise 6 echo least-squares fit (6LS) and (2) a voxel-wise 2 echo point T2(*) determination (2MM). The third method used median ligament signal intensity and a single nonlinear least-squares fit (6LSROI) instead of a voxel-wise basis. The resulting median T2(*) values of the PCL and computational time were compared. The median T2(*) values were 42% higher using the 2MM compared to the 6LS method (p<0.0001). However, a strong correlation was found for the median T2(*) values between the 2MM and 6LS methods (R(2)=0.80). The median T2(*) values were not significantly different between the 6LS and 6LSROI methods (p=0.519). Using the 2MM (which provides a regional map) and the 6LSROI (which efficiently provides the median T2(*) value) methods in tandem would take only minutes of post-processing computational time compared to the 6LS method (~540 min), and hence would facilitate clinical application of T2(*) maps to predict ligament structural properties as a patient outcome measure.

Basic science of anterior cruciate ligament injury and repair.

Injury to the anterior cruciate ligament (ACL) is one of the most devastating and frequent injuries of the knee. Surgical reconstruction is the current standard of care for treatment of ACL injuries in active patients. The widespread adoption of ACL reconstruction over primary repair was based on early perception of the limited healing capacity of the ACL. Although the majority of ACL reconstruction surgeries successfully restore gross joint stability, post-traumatic osteoarthritis is commonplace following these injuries, even with ACL reconstruction. The development of new techniques to limit the long-term clinical sequelae associated with ACL reconstruction has been the main focus of research over the past decades. The improved knowledge of healing, along with recent advances in tissue engineering and regenerative medicine, has resulted in the discovery of novel biologically augmented ACL-repair techniques that have satisfactory outcomes in preclinical studies. This instructional review provides a summary of the latest advances made in ACL repair. Cite this article: Bone Joint Res 2014;3:20-31.

Loss of extracellular matrix from articular cartilage is mediated by the synovium and ligament after anterior cruciate ligament injury.

OBJECTIVE: Post-traumatic osteoarthritis (PTOA) occurs after anterior cruciate ligament (ACL) injury. PTOA may be initiated by early expression of proteolytic enzymes capable of causing degradation of the articular cartilage at time of injury. This study investigated the production of three of these key proteases in multiple joint tissues after ACL injury and subsequent markers of cartilage turnover. METHODS: ACL transection was performed in adolescent minipigs. Collagenase (MMP-1 and MMP-13) and aggrecanase (ADAMTS-4) gene expression changes were quantified in the articular cartilage, synovium, injured ligament, and the provisional scaffold at days 1, 5, 9, and 14 post-injury. Markers of collagen degradation (C2C), synthesis (CPII) and aggrecan synthesis (CS 846) were quantified in the serum and synovial fluid. Histologic assessment of the cartilage integrity (OARSI scoring) was also performed. RESULTS: MMP-1 gene expression was upregulated in the articular cartilage, synovium and ligament after ACL injury. MMP-13 expression was suppressed in the articular cartilage, but upregulated 100-fold in the synovium and ligament. ADAMTS-4 was upregulated in the synovium and ligament but not in the articular cartilage. The concentration of collagen degradation fragments (C2C) in the synovial joint fluid nearly doubled in the first five days after injury. CONCLUSION: We conclude that upregulation of genes coding for proteins capable of degrading cartilage ECM is seen within the first few days after ACL injury, and this response is seen not only in chondrocytes, but also in cells in the synovium, ligament and provisional scaffold.

Mesenchymal stem cells from the retropatellar fat pad and peripheral blood stimulate ACL fibroblast migration, proliferation, and collagen gene expression.

Mesenchymal stem cells (MSCs) have been of recent interest as adjuncts for ligament repair. However, the effect of these cells on the resident ligament fibroblasts has not yet been defined. In this study, we hypothesized that co-culture of MSCs and ligament fibroblasts would result in increases in the proliferative rate of the ligament fibroblasts and their expression of collagen-related genes, as well as differentiation of the MSCs down a fibroblastic pathway. In addition, we hypothesized that these effects would be dependent on the source of the MSCs. Porcine MSCs were isolated from both the retro-patellar fat pad (ADSCs) and the peripheral blood (PBMCs) and co-cultured with porcine anterior cruciate ligament (ACL) fibroblasts. Fibroblast migration, proliferation, and collagen gene expression were evaluated at time points up to 14 days. ADSCs had a greater effect on stimulating ACL-fibroblast proliferation and procollagen production, while PBMCs were more effective in stimulating ligament fibroblast migration. In addition, co-culture with the ACL fibroblasts led to significant increases in collagen gene expression for ADSCs, suggesting a differentiation of these cells down a fibroblastic pathway during the co-culture period. This was not seen for the PBMCs. Thus, the effects of MSCs on in situ ACL fibroblasts were found to be source dependent, and the choice of MSC source should take into account the different performance characteristic of each type of MSC.

Histologic Predictors of Maximum Failure Loads Differ between the Healing ACL and ACL Grafts after 6 and 12 Months In Vivo.

BACKGROUND: Bio-enhanced ACL repair, where the suture repair is supplemented with a biological scaffold, is a promising novel technique to stimulate healing after ACL rupture. However, the histological properties of a successfully healing ACL and how they relate to the mechanical properties have not been fully described. HYPOTHESIS/PURPOSE: The purpose of the study was to determine which histological features best correlated with the mechanical properties of the healing ACL repairs and ACL grafts in a porcine model at six and twelve months after injury. STUDY DESIGN: Controlled laboratory study. METHODS: Forty-eight Yucatan mini-pigs underwent ACL transection followed by: 1) conventional ACL reconstruction with bone-patellar tendon-bone (BPTB) allograft, 2) bio-enhanced ACL reconstruction with BPTB allograft using a bioactive scaffold, or 3) bio-enhanced ACL repair using the same bioactive scaffold. After 6 and 12 months of healing, structural properties of the ACL or graft (yield & failure load, linear stiffness) were measured. Following mechanical testing, ACL specimens were histologically analyzed for cell and vascular density and qualitatively assessed using the advanced Ligament Maturity Index. RESULTS: We found that after six months of healing, the cellular organization sub-score was most predictive of yield load (r2=0.98), maximum load (r2=0.89) and linear stiffness (r2=0.95) of the healing ACL, while at 12 months, the collagen sub-score (r2=0.68) became the best predictor of maximum load. For ACL grafts, the reverse was true, with the collagen sub-score predictive of yield and maximum loads at six months (r2=0.55), and graft cellularity predictive of maximum load of the graft at 12 months (r2=0.50). CONCLUSIONS: These findings suggest there may be key biologic differences in development and maintenance of ACL tissue after repair or reconstruction with early ligament function dependent on cellular population of the repair but early graft function dependent on the maintenance of organized collagen.

Comparison of real and idealized cetacean flippers.

When a phenomenon in nature is mimicked for practical applications, it is often done so in an idealized fashion, such as representing the shape found in nature with convenient, piece-wise smooth mathematical functions. The aim of idealization is to capture the advantageous features of the natural phenomenon without having to exactly replicate it, and it is often assumed that the idealization process does in fact capture the relevant geometry. We explored the consequences of the idealization process by creating exact scale models of cetacean flippers using CT scans, creating corresponding idealized versions and then determining the hydrodynamic characteristics of the models via water tunnel testing. We found that the majority of the idealized models did not exhibit fluid dynamic properties that were drastically different from those of the real models, although multiple consequences resulting from the idealization process were evident. Drag performance was significantly improved by idealization. Overall, idealization is an excellent way to capture the relevant effects of a phenomenon found in nature, which spares the researcher from having to painstakingly create exact models, although we have found that there are situations where idealization may have unintended consequences such as one model that exhibited a decrease in lift performance.

Storage conditions do not have detrimental effect on allograft collagen or scaffold performance.

Musculoskeletal allografts are a valuable alternative to autograft tissue in orthopaedic surgeries. However, the effects of the allografts' storage history on the collagen and subsequent allograft scaffold properties are unknown. In this study, we hypothesized that freezing and refrigeration of allografts for 1 week would alter the biologic performance and mechanical properties of the allograft collagen. Allograft collagen was characterized by SDS-PAGE migration pattern, amino acid profile and measured denaturation. Scaffolds made from allograft collagen were evaluated for fibroblast proliferation, platelet activation and scaffold retraction. Collagen gelation kinetics (elastic and inelastic moduli and the viscous-elastic transition point) were also evaluated. Fibroblast proliferation, platelet activation and scaffold retraction results showed only minor, though statistically significant, differences between the storage groups. In addition, there were no significant differences in rheological properties or collagen biochemistry. In conclusion, this study suggests that freezing or refrigeration for 1 week does not appear to have any detrimental effect on the mechanical properties and biologic performance of the collagen within allografts.

Injection temperature significantly affects in vitro and in vivo performance of collagen-platelet scaffolds.

Collagen-platelet composites have recently been successfully used as scaffolds to stimulate anterior cruciate ligament (ACL) wound healing in large animal models. These materials are typically kept on ice until use to prevent premature gelation; however, with surgical use, placement of a cold solution then requires up to an hour while the solution comes to body temperature (at which point gelation occurs). Bringing the solution to a higher temperature before injection would likely decrease this intra-operative wait; however, the effects of this on composite performance are not known. The hypothesis tested here was that increasing the temperature of the gel at the time of injection would significantly decrease the time to gelation, but would not significantly alter the mechanical properties of the composite or its ability to support functional tissue repair. Primary outcome measures included the maximum elastic modulus (stiffness) of the composite in vitro and the in vivo yield load of an ACL transection treated with an injected collagen-platelet composite. In vitro findings were that injection temperatures over 30 degrees C resulted in a faster visco-elastic transition; however, the warmed composites had a 50% decrease in their maximum elastic modulus. In vivo studies found that warming the gels prior to injection also resulted in a decrease in the yield load of the healing ACL at 14 weeks. These studies suggest that increasing injection temperature of collagen-platelet composites results in a decrease in performance of the composite in vitro and in the strength of the healing ligament in vivo and this technique should be used only with great caution.

The tissue plasminogen activator gene promoter: a novel tool for radiogenic gene therapy of the prostate?

BACKGROUND: Radiation therapy is a treatment modality routinely used in cancer management so it is not unexpected that radiation-inducible promoters have emerged as an attractive tool for controlled gene therapy. The human tissue plasminogen activator gene promoter (t-PA) has been proposed as a candidate for radiogenic gene therapy, but has not been exploited to date. The purpose of this study was to evaluate the potential of this promoter to drive the expression of a reporter gene, the green fluorescent protein (GFP), in response to radiation exposure. METHODS: To investigate whether the promoter could be used for prostate cancer gene therapy, we initially transfected normal and malignant prostate cells. We then transfected HMEC-1 endothelial cells and ex vivo rat tail artery and monitored GFP levels using Western blotting following the delivery of single doses of ionizing radiation (2, 4, 6 Gy) to test whether the promoter could be used for vascular targeted gene therapy. RESULTS: The t-PA promoter induced GFP expression up to 6-fold in all cell types tested in response to radiation doses within the clinical range. CONCLUSIONS: These results suggest that the t-PA promoter may be incorporated into gene therapy strategies driving therapeutic transgenes in conjunction with radiation therapy.

Direct observation of the phenomenology of a solid thermal explosion using time-resolved proton radiography.

We present a new phenomenology for burn propagation inside a thermal explosion based on dynamic radiography. Radiographic images were obtained of an aluminum cased solid cylindrical sample of a plastic bonded formulation of octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine. The phenomenology observed is ignition followed by cracking in the solid accompanied by the propagation of a radially symmetric front of increasing proton transmission. This is followed by a further increase in transmission through the sample, ending after approximately 100 micros. We show that these processes are consistent with the propagation of a convective burn front followed by consumption of the remaining solid by conductive particle burning.

Role played by BRCA1 in transcriptional regulation in response to therapy.

BRCA1 (breast-cancer susceptibility gene 1) is a tumour suppressor, implicated in the hereditary predisposition to breast and ovarian cancer. BRCA1 has been implicated in a number of cellular processes including DNA repair and recombination, cell cycle checkpoint control, chromatin remodelling and ubiquitination. In addition, substantial data now exist to suggest a role for BRCA1 in transcriptional regulation; BRCA1 has been shown to interact with the Pol II holoenzyme complex and to interact with multiple transcription factors, such as p53 and c-Myc. We have previously identified a range of BRCA1 transcriptional targets and have linked these to specific cellular pathways, including cell cycle checkpoint activation and apoptosis. Current research is focused on the transcriptional mechanisms that underpin the association of BRCA1 deficiency with increased sensitivity to DNA damage-based chemotherapy and resistance to spindle poisons.

The central ACL defect as a model for failure of intra-articular healing.

Intra-articular soft tissues, such as the anterior cruciate ligament (ACL), fail to heal in contrast to the extra-articular medial collateral ligament (MCL), which undergoes classic healing. The goal of this study was to validate a model for failure of intra-articular healing that could be used in the future to test new repair strategies. We conducted a two-part experiment, the first part ex vivo, and the second in vivo. Our initial ex vivo experiments were used to determine the optimal width of the central defect in the canine ACL that would produce reproducible structural properties at time zero. The second experimental series used this optimal scalpel blade width to create a central defect in the canine ACL followed by measurement of structural properties in the ACL after either a 3- or 6-week in vivo healing period. A 3.5-mm beaver blade resulted in a maximum tolerated load of 56.8 +/- 4.7% (mean +/- SEM) of control at time zero. After the 3- and 6-week in vivo healing periods, the maximum load was 74.6 +/- 5.3 at 3 weeks and 64.9 +/- 3.8% at 6 weeks compared to control. Thus, biomechanical parameters tested at 6 weeks after creation of a defect showed no significant gains from defects tested immediately after the creation of injury. The centrally placed ACL defect in this canine model demonstrates failure to mechanically heal, which should prove suitable for future in vivo evaluation of the biomechanical and histological response to tissue engineering repair strategies for intra-articular soft tissues.

The effect of thrombin on ACL fibroblast interactions with collagen hydrogels.

Premature loss of provisional scaffold formation has been identified as one of the factors responsible for poor healing of intraarticular tissues. To address this deficiency, substitute provisional scaffolds are being developed. The function of these scaffolds can be enhanced by the addition of specific extracellular matrix proteins. In this study, it was hypothesized that the addition of thrombin to a provisional scaffold material would result in increases in cell proliferation, collagen production, and cell migration within the scaffold. These three parameters are thought to be critical components of wound healing. Gels containing fibrin and collagen supplemented with either 0, 10.5, 21, or 42 U/mL of thrombin were placed in contact with explants of tissue from the anterior cruciate ligament. The addition of thrombin stimulated cell migration at low concentrations and impaired migration at higher concentrations, and had no significant effect on cell proliferation or collagen production. The use of all concentrations of thrombin resulted in mechanically weaker gels. Thus, the use of thrombin to optimize a collagen-platelet rich plasma (PRP) provisional scaffold must be done with caution, and use of high concentrations of thrombin (>42 IU/mL) should be avoided specifically in situations where gel strength or cell ingrowth is important. Use of low concentrations of thrombin (10.5 IU/mL) may be beneficial in applications where a faster set time and enhanced cell migration are desirable and the gel mechanical strength is of secondary importance.

The migration of cells from the ruptured human anterior cruciate ligament into collagen-glycosaminoglycan regeneration templates in vitro.

Guided tissue regeneration of the ruptured anterior cruciate ligament (ACL) offers the potential benefits of retaining the complex footprints of the ACL and the proprioceptive nerve fibers of the tissue. For this approach to be successful, ACL cells must retain the ability to migrate into an adjacent regeneration template, or scaffold, after ligament rupture. Ruptured ACLs were obtained from the knees of four men, ages 25-35, at the time of ACL reconstruction. Explants of ACL tissue were taken from three locations along the longitudinal axis of the remnant: the rupture site, the middle of the remnant, and far from the rupture site. These three areas have been found to be distinct histologically, with the region far from the rupture site having a histologic appearance similar to the intact ligament. Explants from each area were cultured in conventional tissue culture dishes (2-D culture) and on porous collagen-glycosaminoglycan (CG) scaffolds. Two-dimensional outgrowth was measured 3 times a week, and the 3-D explant/scaffold constructs were examined at 1, 2, 3 and 4 weeks to assess outgrowth of cells into the scaffold. The cell number density and expression of a-smooth muscle actin (SMA) were determined at each time point. The decrease in the diameter of the scaffolds and non-seeded controls were determined as a function of time in culture. The outgrowth of cells onto the tissue culture dishes was observed to begin as early as 3 days and as late as 21 days, with outgrowth first detected at an average of 6.8 +/- 2.0 days after explantation. In general, there was a larger area of outgrowth at the 2-week time point from explants with higher cell number density and higher blood vessel density. The 2-week area of outgrowth also correlated with the percentage of SMA-positive cells in the explant. In the experimental constructs with CG scaffolds, fibroblasts were noted to migrate from the human ACL explants into the templates at the earliest time point recorded (I week). The migration and proliferation of cells from the explants in the CG matrices resulted in an increase in the cell density in the scaffolds with time. There was a significant effect of the location from which the explant was taken on cell density in the scaffold, with a higher density of cells migrating from the explants from the rupture site of the ACL specimens. The percentage of cells staining positive for the SMA isoform varied from 0 to 50% of cells in the scaffold. Scaffolds co-cultured with explants showed a reduction in diameter that was significantly affected by time in culture and the location in the ACL from which the explant was taken. The percentage contraction attributed to the cells was 15% at 2 weeks, and increased to 27% for the injury-zone explant at 4 weeks. There was a significant correlation of the cell-mediated contraction of the matrices at 4 weeks with the cell density in the scaffolds, but not with the number of SMA-positive cells in the scaffolds. These data demonstrate that cells in the human ACL retain their ability to migrate into an adjacent CG scaffold in vitro, weeks after complete rupture. Moreover, the ACL-derived cells can express a contractile actin isoform and can contract a CG analog of extracellular matrix.

The chemopotentiation of cisplatin by the novel bioreductive drug AQ4N.

AQ4N is a bioreductive drug that can significantly enhance the anti-tumour effect of radiation and cyclophosphamide. The aim of this study was to examine the ability of AQ4N to potentiate the anti-tumour effect of cisplatin and to compare it to the chemopotentiation effect of tirapazamine. In the T50/80 murine tumour model, AQ4N (50-100 mg/kg) was administered 30 min, 2.5 or 6 h prior to cisplatin (4 mg/kg or 8 mg/kg); this produced an anti-tumour effect that was approximately 1.5 to 2 times greater than that achieved by a single 4 or 8 mg/kg dose of cisplatin. Tirapazamine (25 mg/kg) administered 2.5 h prior to cisplatin (4 mg/kg) resulted in a small increase in anti-tumour efficacy. AQ4N was also successful in enhancing the anti-tumour effect of cisplatin in the SCCVII and RIF-1 murine tumour models. This resulted in an increased cell kill of greater than 3 logs in both models; this was a greater cell kill than that observed for tirapazamine with cisplatin. Combination of cisplatin with AQ4N or tirapazamine resulted in no additional bone marrow toxicity compared to cisplatin administered alone. In conclusion, AQ4N has the potential to improve the clinical efficacy of cisplatin.

Attention-dependent suppression of distracter visual input can be cross-modally cued as indexed by anticipatory parieto-occipital alpha-band oscillations.

Recent studies show that in addition to enhancing neural processing for attentionally relevant stimuli, selective attention also operates by suppressing the processing of distracter stimuli. When subjects are pre-cued to selectively deploy attention during voluntary (endogenous) attentional tasks, these mechanisms can be set up in advance of actual stimulus processing. That is, the brain can be placed in a biased attentional state. Two recent cueing studies have provided evidence for the deployment of such biased attentional states [J.J. Foxe, G.V. Simpson, S.P. Ahlfors, Neuroreport 9 (1998) 3929-3933; M.S. Worden, J.J. Foxe, N. Wang, G.V. Simpson, J. Neurosci. 20:RC63 (2000) 1-6]. Specifically, these studies implicated oscillatory activity in the alpha frequency-band (8-14 Hz) as an anticipatory mechanism for suppressing distracter visual stimulation. The current study extends these findings by showing that this alpha-suppressive effect is also invoked by cross-modal cues. Auditory symbolic cues were used in an intermodal attention task, to direct subjects' attention to a subsequent task in either the visual or auditory modality. Cueing attention to the auditory features of the imminent task stimuli resulted in significantly higher parieto-occipital alpha amplitude in the period preceding onset of this stimulus than when attention was cued to the visual features. Topographic mapping suggests that this effect is generated in regions of the inferior parietal cortex, areas that have been repeatedly implicated in the engagement and maintenance of visual attention. Taken together, the results of this series of studies suggest that these parietal regions are capable of integrating sensory cues from multiple sensory modalities in order to program the subsequent deployment of visual attention.

Distribution of smooth muscle actin-containing cells in the human meniscus.

This is the first report of a contractile actin isoform, a-smooth muscle actin (SMA), in the cells of the human meniscus that lacked meniscal tears based on gross anatomical appearance. Approximately 25% of the cells in the tissue contained SMA by immunohistochemistry. Most of the SMA-positive cells were chondrocytic in morphology.

The presence of smooth muscle actin in fibroblasts in the torn human rotator cuff.

The rotator cuff frequently sustains athletic and occupational injury, often resulting in chronic pain and disability. However, despite the high incidence of such shoulder problems, the pathophysiology of rotator cuff injury and healing has not yet been fully elucidated. The notable finding of this study was the presence of a contractile actin isoform, alpha-smooth muscle actin (SMA), in nonvascular cells in all of the seven torn human rotator cuff specimens evaluated immunohistochemically. Up to 95% of cells in any one region, and over 95% of elongated cells found in association with crimped collagen, contained SMA. Most of the cells staining positive for SMA in these sections had morphological features of the fibroblast, though a small number were chondrocyte-like. Treatment of cells growing out from human rotator cuff explants with TGF-beta1 significantly increased the amount of SMA evaluated by Western blot analysis. PDGF-BB and IFN-gamma had no effect on the cell content of SMA. This is the first documentation of the presence of SMA-positive cells in the human rotator cuff tendon. SMA has been found in a number of other healing connective tissues including skin, ligament, meniscus, cartilage, and other types of tendon. Of importance are previous findings that SMA-positive cells can contract a collagen-glycosaminoglycan analog of extracellular matrix in vitro. The results of the present study thus suggest that SMA-containing cells could contribute to the retraction of the torn ends of a ruptured rotator cuff and play an important role in healing.