A Mechanistic and Preclinical Assessment of BioRestore Bioactive Glass as a Synthetic Bone Graft Extender and Substitute for Osteoinduction and Spine Fusion

STUDY DESIGN

Preclinical animal study.

OBJECTIVE

Evaluate the osteoinductivity and bone regenerative capacity of BioRestore bioactive glass.

SUMMARY OF BACKGROUND DATA

BioRestore is a Food and Drug Administration (FDA)-approved bone void filler that has not yet been evaluated as a bone graft extender or substitute for spine fusion.

METHODS

In vitro and in vivo methods were used to compare BioRestore with other biomaterials for the capacity to promote osteodifferentiation and spinal fusion. The materials evaluated (1) absorbable collagen sponge (ACS), (2) allograft, (3) BioRestore, (4) Human Demineralized Bone Matrix (DBM), and (5) MasterGraft. For in vitro studies, rat bone marrow-derived stem cells (BMSC) were cultured on the materials in either standard or osteogenic media (SM, OM), followed by quantification of osteogenic marker genes (Runx2, Osx, Alpl, Bglap, Spp1) and alkaline phosphatase (ALP) activity. Sixty female Fischer rats underwent L4-5 posterolateral fusion (PLF) with placement of 1 of 5 implants: (1) ICBG from syngeneic rats; (2) ICBG+BioRestore; (3) BioRestore alone; (4) ICBG+Allograft; or (5) ICBG+MasterGraft. Spines were harvested 8 weeks postoperatively and evaluated for bone formation and fusion via radiography, blinded manual palpation, microCT, and histology.

RESULTS

After culture for 1 week, BioRestore promoted similar expression levels of Runx2 and Osx to cells grown on DBM. At the 2-week timepoint, the relative ALP activity for BioRestore-OM was significantly higher (P<0.001) than that of ACS-OM and DBM-OM (P<0.01) and statistically equivalent to cells grown on allograft-OM. In vivo, radiographic and microCT evaluation showed some degree of bridging bone formation in all groups tested, with the exception of BioRestore alone, which did not produce successful fusions.

CONCLUSIONS

This study demonstrates the capacity of BioRestore to promote osteoinductivity in vitro. In vivo, BioRestore performed similarly to commercially available bone graft extender materials but was incapable of producing fusion as a bone graft substitute.

LEVEL OF EVIDENCE

Level V.

Epidemiology of patellar dislocations in the United States from 2001 to 2020: results of a national emergency department database

OBJECTIVES

Recent studies have shown an increasing incidence of patellar dislocations among children and adolescents. Updated, population-based studies of all patellar dislocations in the United States (US), however, are lacking. This study investigated recent trends in injury rates and demographics among patients sustaining patellar dislocations in the US from 2001 to 2020.

METHODS

This descriptive epidemiologic study retrospectively analyzed the National Electronic Injury Surveillance System (NEISS) database to identify cases of acute patellar dislocations presenting to US Emergency Departments (EDs) from 2001 to 2020. Annual, overall, and age-adjusted incidence rates (IRs, expressed per 100,000 at-risk person-years) and additional patient/injury characteristics were analyzed. Average annual percent change (AAPC) estimates are presented to indicate the magnitude/direction of trends in annual injury rates.

RESULTS

An estimated total of 159,529 patellar dislocations occurred over the study period for an overall IR of 2.58 (95% CI = 2.04-3.12). Accounting for population growth, the overall annual incidence increased significantly from 2.61 in 2001 to 3.0 in 2020 (AAPC = 2.8, p < 0.0001). When considering sex and age, statistically significant increases in annual IRs were observed among males aged 10-19 years (AAPC = 3.8, p < 0.0001), females aged 10-19 years (AAPC = 5.3, p < 0.0001), and females aged 20-29 years (AAPC = 3.5, p = 0.0152), while no significant changes were observed in any other age groups. Two-thirds of patellar dislocations involved sports-related injury mechanisms. The annual incidence of both sports-related and non-sports-related injuries increased significantly over the study period (sports-related: AAPC = 2.6, p = 0.0001; non-sports-related: AAPC = 3.4, p = 0.0001). Athletic patellar dislocations occurred most commonly in basketball and dance.

CONCLUSION

The number of patients sustaining patellar dislocations is increasing in the US. Similar increasing trends were observed in both males and females aged 10-19 years, whereas injury rates increased in the third decade only among females. A large percentage of injuries occur during athletic activity, but both sports- and non-sports-related patellar dislocations are on the rise.

Epidemiology of C2 fractures in the United States: A National Electronic Injury Surveillance System database study

Introduction

C2 fractures are one of the most common traumatic injuries of the cervical spine, with high rates of morbidity and mortality. Current literature on the incidence of C2 fractures is limited to populations outside of the United States (US), prior to 2014, or specific age cohorts. The purpose of this study is to report the incidence rate (IR) of C2 fractures and associated patient demographics in the US between 2002 and 2021 using the National Electronic Injury Surveillance System (NEISS) database.

Methods

This study analyzed the NEISS database to identify cases of C2 fractures presenting to US Emergency Departments (EDs) from 2002 to 2021. Annual and overall numbers of fractures, IR, and patient demographics were analyzed. IR is expressed as the number of fractures per 100,000 person-years at risk (PYR). Patients were split into three different age groups for comparison (children and young adults, 0-64 years; older adults, 65-79 years; elderly individuals, 80 + years).

Results

A national estimate of n = 72,764 patients (95% confidence interval [CI] = 54,371-91,156) presented to US EDs with a C2 fracture (IR was 1.17/PYR; 95% CI = 0.87-1.46), and elderly individuals had the highest IR overall (IR = 15.9; P < 0.05). The IR of C2 fractures between 2002 and 2021, reported as average annual percent change (AAPC), increased significantly, regardless of age or sex (AAPC = 10.9; 95% CI = 6.3-15.6; P < 0.0001).

Conclusion

C2 fractures occur at higher rates than previous years, with especially high IR in elderly individuals. Emphasis of public health efforts toward osteoporosis and coordination difficulties in elderly individuals would likely significantly reduce the overall IR of these injuries.

Trends and epidemiology of knee extensor mechanism injuries presenting to United States emergency departments from 2001 to 2020

OBJECTIVES

Injuries to the native extensor mechanism (EM) of the knee are potentially disabling and often require surgical treatment. Large-scale, updated epidemiological data on these injuries is lacking. The objective of the current study was to examine recent trends in EM injuries presenting to United States (US) Emergency Departments (EDs) over the last 20 years using a nationally representative sample.

METHODS

This study retrospectively analyzed the National Electronic Injury Surveillance System (NEISS) database to identify cases of EM injuries (defined as either a quadriceps tendon rupture, a patella fracture, or a patellar tendon rupture) presenting to EDs in the US from 2001 to 2020.

RESULTS

During the study period, an estimated 214,817 EM injuries occurred in an at-risk population of 6,183,899,410 person-years for an overall incidence rate of 3.47 per 100,000 person-years. Patella fractures (PFs) were the most common injury type, representing 77.5% of all EM injuries (overall incidence rate: 2.69), followed by patellar tendon ruptures (PTRs; 13.5%; incidence: 0.48) and quadriceps tendon ruptures (QTRs; 9%; incidence: 0.31). Demographic characteristics and mechanisms of injury differed between injury types. Annual incidence rates increased significantly during the study period for all EM injury types, with PTRs demonstrating the largest relative increase (average annual percent increase: PF, 2.8%; PTR, 7.2%; QTR, 5.3%). Accounting for population growth yielded an increasing incidence of all EM injuries combined from 3.65 in 2001 to 4.9 in 2020. The largest relative increases in incidence rates were observed in older age groups.

CONCLUSION

Extensor mechanism injuries of the knee are increasing in the US, which likely reflects an aging and more active population. These types of injuries are associated with substantial functional impairment and recent increases in incidence rates highlight the need for injury prevention and management strategies.

Knowledge of radiation exposure associated with common trauma imaging modalities among orthopaedic surgeons, emergency medicine physicians, and general surgeons in the United States

BACKGROUND

Few contemporary studies have assessed physicians' knowledge of radiation exposure associated with common imaging studies, especially in trauma care. The purpose of this study was to assess the knowledge of physicians involved in caring for trauma patients regarding the effective radiation doses of musculoskeletal (MSK) imaging studies routinely utilized in the trauma setting.

METHODS

An electronic survey was distributed to United States orthopaedic surgery, general surgery, and emergency medicine (EM) residency programs. Participants were asked to estimate the radiation dose for common imaging modalities of the pelvis, lumbar spine, and lower extremity, in terms of chest X-ray (CXR) equivalents. Physician estimates were compared to the true effective radiation doses. Additionally, participants were asked to report the frequency of discussing radiation risk with patients.

RESULTS

A total of 218 physicians completed the survey; 102 (46.8%) were EM physicians, 88 (40.4%) were orthopaedic surgeons, and 28 (12.8%) were general surgeons. Physicians underestimated the effective radiation doses of nearly all imaging modalities, most notably for pelvic computed tomaography (CT) (median 50 CXR estimation vs. 162 CXR actual) and lumbar CT (median 50 CXR estimation vs. 638 CXR actual). There was no difference between physician specialties regarding estimation accuracy (P=0.133). Physicians who regularly discussed radiation risks with patients more accurately estimated radiation exposure (P=0.007).

CONCLUSION

The knowledge among orthopaedic and general surgeons and EM physicians regarding the radiation exposure associated with common MSK trauma imaging is lacking. Further investigation with larger scale studies is warranted, and additional education in this area may improve care.

Accuracy of self-reported opioid use in orthopaedic trauma patients

PURPOSE

Opioids have long been a mainstay of treatment for pain in patients with orthopaedic injuries, but little is known about the accuracy of self-reported narcotic usage in orthopaedic trauma. The purpose of this study is to evaluate the accuracy of self-reported opioid usage in orthopaedic trauma patients.

METHODS

A retrospective review of all new patients presenting to the orthopaedic trauma clinic of a level 1 trauma centre with a chief complaint of recent orthopaedic-related injury over a 2-year time frame was conducted. Participants were administered a survey inquiring about narcotic usage within the prior 3 months. Responses were cross-referenced against a query of a statewide prescription drug monitoring program system.

RESULTS

The study comprised 241 participants; 206 (85.5%) were accurate reporters, while 35 (14.5%) were inaccurate reporters. Significantly increased accuracy was associated with hospital admission prior to clinic visit (β = - 1.33; χ² = 10.68, P < 0.01; OR: 0.07, 95% CI 0.01-0.62). Decreased accuracy was associated with higher pre-visit total morphine equivalent dose (MED) (β = 0.002; χ² = 11.30, P < 0.01), with accurate reporters having significantly lower pre-index visit MED levels compared to underreporters (89.2 ± 208.7 mg vs. 249.6 ± 509.3 mg; P = 0.04). An Emergency Department (ED) visit prior to the index visit significantly predicted underreporting (β = 0.424; χ² = 4.28, P = 0.04; OR: 2.34, 95% CI 1.01-5.38).

CONCLUSION

This study suggests that most new patients presenting to an orthopaedic trauma clinic with acute injury will accurately report their narcotic usage within the preceding 3 months. Prior hospital admissions increased the likelihood of accurate reporting while higher MEDs or an ED visit prior to the initial visit increased the likelihood of underreporting.

Sex-based Difference in Response to Recombinant Human Bone Morphogenetic Protein-2 in a Rat Posterolateral Fusion Model

STUDY DESIGN

This was a preclinical study.

OBJECTIVE

Evaluate sex-dependent differences in the bone healing response to recombinant human bone morphogenetic protein-2 (rhBMP-2) in a rat posterolateral spinal fusion model.

SUMMARY OF BACKGROUND DATA

Minimal and conflicting data exist concerning potential sex-dependent differences in rhBMP-2-mediated bone regeneration in the context of spinal fusion.

MATERIALS AND METHODS

Forty-eight female and male Sprague-Dawley rats (N=24/group), underwent L4-L5 posterolateral fusion with bilateral placement of an absorbable collagen sponge, each loaded with 5 µg of bone morphogenetic protein-2 (10 µg/animal). At eight weeks postoperative, 10 specimens of each sex were tested in flexion-extension with quantification of range of motion and stiffness. The remaining specimens were evaluated for new bone growth and successful fusion via radiography, blinded manual palpation and microcomputed tomography (microCT). Laboratory microCT quantified bone microarchitecture, and synchrotron microCT examined bone microstructure at the 1 µm level.

RESULTS

Manual palpation scores differed significantly between sexes, with mean fusion scores of 2.4±0.4 in females versus 3.1±0.6 in males ( P <0.001). Biomechanical stiffness did not differ between sexes, but range of motion was significantly greater and more variable for females versus males (3.7±5.6° vs. 0.27±0.15°, P <0.005, respectively). Laboratory microCT showed significantly smaller volumes of fusion masses in females versus males (262±87 vs. 732±238 mm 3 , respectively, P <0.001) but significantly higher bone volume fraction (0.27±0.08 vs. 0.12±0.05, respectively, P <0.001). Mean trabecular thickness was not different, but trabecular number was significantly greater in females (3.1±0.5 vs. 1.5±0.4 mm -1 , respectively, P <0.001). Synchrotron microCT showed fine bone structures developing in both sexes at the eight-week time point.

CONCLUSIONS

This study demonstrates sex-dependent differences in bone regeneration induced by rhBMP-2. Further investigation is needed to uncover the extent of and mechanisms underlying these sex differences, particularly at different doses of rhBMP-2.

Funding has no effect on clinical outcomes of total joint arthroplasty emerging technologies: a systematic review of bibliometrics and conflicts of interest

Background

The use of new total joint arthroplasty technologies, including patient-specific implants/instrumentation (PSI), computer-assisted (CA), and robotic-assisted (RA) techniques, is increasing. There is an ongoing debate regarding the value provided and potential concerns about conflicts of interest (COI).

Methods

PRISMA guidelines were followed. PubMed, MEDLINE, and Web of Science databases were searched for total hip and knee arthroplasties, unicompartmental knee arthroplasties (UKA), PSI, CA, and RA. Bibliometric data, financial COI, clinical/functional scores, and patient-reported outcomes were assessed.

Results

Eighty-seven studies were evaluated, with 35 (40.2%) including at least one author reporting COI, and 13 (14.9%) disclosing industry funding. COI and industry funding had no significant effects on outcomes (P = 0.682, P = 0.447), and there were no significant effects of conflicts or funding on level of evidence (P = 0.508, P = 0.826). Studies in which author(s) disclosed COI had significantly higher relative citation ratio (RCR) and impact factor (IF) than those without (P < 0.001, P = 0.032). Subanalysis demonstrated RA and PSI studies were more likely to report COI or industry funding (P = 0.045). RA (OR = 6.31, 95% CI: 1.61–24.68) and UKA (OR = 9.14, 95% CI: 1.43–58.53) had higher odds of reporting favorable outcomes than PSI.

Conclusions

Author COIs (about 40%) may be lower than previously reported in orthopedic technologies/techniques reviews. Studies utilizing RA and PSI were more likely to report COI, while RA and UKA studies were more likely to report favorable outcomes than PSI. No statistically significant association between the presence of COIs and/or industry funding and the frequency of favorable outcomes or study level of evidence was found.

Level of evidence

Level V Systematic Review

Supplementary Information

The online version contains supplementary material available at 10.1186/s42836-022-00146-3.

Effects of veterans' mental health service-connections on patient-reported outcomes following total joint arthroplasty

Background

Studies report poor outcomes of elective orthopaedic surgeries among civilian patients receiving Workers' Compensation (WC). However, little is known about surgical outcomes in veterans receiving similar benefits through the Veterans Affairs (VA) service-connected (SC) disability compensation program.

Methods

Veterans undergoing primary total hip arthroplasty (THA) or total knee arthroplasty (TKA) at a VA Medical Center between 07/2019-12/2021 were analyzed by SC status. Outcomes were evaluated using Hip disability and Osteoarthritis Outcome Score for Joint Replacement (HOOS-JR) and Knee injury and Osteoarthritis Outcome Score for Joint Replacement (KOOS-JR) scores collected preoperatively and at 2- and 12-months postoperatively. Repeated measures mixed models were used to test for the effect of SC on HOOS-JR/KOOS-JR scores, controlling for baseline age, sex, and Charlson Comorbidity Index (CCI). SC and baseline joint function (stratified into quartiles using baseline HOOS-JR/KOOS-JR scores) were analyzed for effects on achieving substantial clinical benefit (SCB) at 12-month follow-up.

Results

The analysis included 67 hips and 142 knees. SC and non-SC (NSC) veterans had similar baseline HOOS-JR/KOOS-JR and CCI. HOOS-JR remained similar between groups through 12 months (79.9 ± 19.2 vs. 82.7 ± 18.8) as did KOOS-JR (70.4 ± 15.6 vs. 74.6 ± 15.3). The designation of any SC and mental health SC reached significance for KOOS-JR (P = 0.034 and P = 0.032, respectively). For HOOS-JR and KOOS-JR, baseline function score quartile significantly influenced final score (P < 0.001), with patients in the lowest quartiles (i.e., worst baseline function) exhibiting significantly greater improvements than patients in higher quartiles.

Conclusions

Mental health SC and high preoperative functional status are variables that may have unfavorable influences on self-reported outcomes of TKA in veteran patients. SC status does not appear to influence the outcomes of THA or the likelihood of achieving SCB after either THA or TKA. Regardless of SC status, most veterans can expect significant clinical improvements after total joint arthroplasty.

A review of current practices in periprosthetic joint infection debridement and revision arthroplasty

BACKGROUND

Periprosthetic joint infection remains a significant challenge for arthroplasty surgeons globally. Over the last few decades, there has been much advancement in terms of treatment and diagnosis, however, the fight rages on. As management of periprosthetic joint infections continues to evolve, it is critical to reflect back on current debridement practices to establish common ground as well as identify areas for future research and improvement. BODY: In order to understand the debridement techniques of periprosthetic joint infections, one must also understand how to diagnose a periprosthetic joint infection. Multiple definitions have been elucidated over the years with no single consensus established but rather sets of criteria. Once a diagnosis has been established the decision of debridement method becomes whether to proceed with single vs two-stage revision based on the probability of infection as well as individual patient factors. After much study, two-stage revision has emerged as the gold standard in the management of periprosthetic infections but single-stage remains prominent with further and further research.

CONCLUSION

Despite decades of data, there is no single treatment algorithm for periprosthetic joint infections and subsequent debridement technique. Our review touches on the goals of debridement while providing a perspective as to diagnosis and the particulars of how intraoperative factors such as intraarticular irrigation can play pivotal roles in infection eradication. By providing a perspective on current debridement practices, we hope to encourage future study and debate on how to address periprosthetic joint infections best.

Screw Thread Configuration Has No Effect on Outcomes of In Situ Fixation for Stable Slipped Capital Femoral Epiphysis

BACKGROUND

No consensus exists regarding the optimal surgical management of slipped capital femoral epiphysis (SCFE). Treatment goals include avoiding slip progression and sequelae such as avascular necrosis (AVN). Factors associated with surgical implants merit further research. This study investigates the effect of screw thread configuration and the number of screws on surgical outcomes.

METHODS

A total of 152 patients undergoing cannulated, stainless steel, in situ screw fixation of SCFE between January 2005 and April 2018 were included. Procedure laterality, screw number and thread configuration (partially threaded/fully threaded), bilateral diagnosis, Loder classification, final follow-up, patient demographics, and endocrinopathy history were analyzed. Primary outcomes were return to the operating room (ROR), AVN, hardware failure/removal, and femoroacetabular impingement (FAI).

RESULTS

Most patients received a single (86.2%), partially threaded (81.6%) screw; most were unilateral (67.8%) and stable (79.6%). Mean follow-up was 2.0±2.7 years, with a 15.8% rate of ROR, 5.3% exhibiting AVN, 6.6% exhibiting FAI, and 9.2% experiencing hardware failure/removal. Number of screws was the sole predictor of ROR [odds ratio (OR)=3.35, 95% confidence interval (CI): 1.18-9.49]. Unstable SCFE increased the odds of AVN (OR=38.44; 95% CI: 4.35-339.50) as did older age (OR=1.43, 95% CI: 1.01-2.03). Female sex increased risk for FAI (OR=4.87, 95% CI: 1.20-19.70), and bilateral SCFE elevated risk for hardware failure/removal versus unilateral SCFE (OR=4.41, 95% CI: 1.39-14.00). Screw thread configuration had no significant effect on any outcome (for each, P ≥0.159).

CONCLUSIONS

Rates of ROR, AVN, FAI, and hardware failure/removal did not differ between patients treated with partially threaded or fully threaded screws. The use of 2 screws was associated with an increased likelihood of ROR. These findings suggest that screw thread configuration has no impact on complication rates, whereas screw number may be an important consideration in SCFE fixation.

LEVEL OF EVIDENCE

Level III-retrospective cohort study.

Reduction in Operating Room Airborne Particle Burden and Time-Dependent Contamination of Sterile Instrument Trays With the Use of a Novel Air Filtration System

Introduction

Postoperative infections represent a substantial burden to patients and healthcare systems. To improve patient care and reduce healthcare expenditures, interventions to reduce surgical infections must be employed. The crystalline C-band ultraviolet (UV-C) air filtration technology (Aerobiotix Inc., Miamisburg, OH, USA) has been designed to reduce airborne bioburden through high-quality filtration and germicidal irradiation. The purpose of this study was to assess the ability of a novel UV-C air filtration device to reduce airborne particle counts and contamination of surgical instrument trays in an operating room (OR) setting.

Materials and methods

Thirty sterile instrument trays were opened in a positive-air-flow OR. The trays were randomly assigned to one of two groups (UV-C or control, n=15 per group). In the UV-C group, the UV-C filtration device was used and in the control, it was not. All trays were opened with the use of a sterile technique and left exposed in the OR for four hours. Air was sampled by a particle counter to measure the numbers of 5µm and 10µm particles. Culture specimens were obtained from the trays to assess for bacterial contamination. Outcome data were collected at 30-minute intervals for the duration of the four-hour study period.

Results

Use of the UV-C device resulted in statistically significant reductions in the numbers of 5µm (average of 64.9% reduction when compared with the control, p<0.001) and 10µm (average of 65.7% reduction when compared with the control, p<0.001)-sized particles detectable in the OR. There was no significant difference in the overall rates of contamination (33.3% in the control group vs. 26.7% in the UV-C group, p=1.0) or the time to contamination (mean survival of 114 minutes in the control group vs. 105 minutes in the UV-C group, p=0.72) of surgical instrument trays with the use of the UV-C device.

Conclusions

The results demonstrate that the UV-C filtration device can successfully reduce airborne bioburden in standard ORs, suggesting that it may have the potential to reduce the risk for wound and hardware infections. Further clinical trials are necessary to better determine the effect of this air filtration system on postoperative infection rates.

Osteoinductivity and biomechanical assessment of a 3D printed demineralized bone matrix-ceramic composite in a rat spine fusion model

We recently developed a recombinant growth factor-free bone regenerative scaffold composed of stoichiometric hydroxyapatite (HA) ceramic particles and human demineralized bone matrix (DBM) particles (HA-DBM). Here, we performed the first pre-clinical comparative evaluation of HA-DBM relative to the industry standard and established positive control, recombinant human bone morphogenetic protein-2 (rhBMP-2), using a rat posterolateral spinal fusion model (PLF). Female Sprague-Dawley rats underwent bilateral L4-L5 PLF with implantation of the HA-DBM scaffold or rhBMP-2. Fusion was evaluated using radiography and blinded manual palpation, while biomechanical testing quantified the segmental flexion-extension range-of-motion (ROM) and stiffness of the fused segments at 8-weeks postoperatively. For mechanistic studies, pro-osteogenic gene and protein expression at 2-days and 1-, 2-, and 8-weeks postoperatively was assessed with another cohort. Unilateral fusion rates did not differ between the HA-DBM (93%) and rhBMP-2 (100%) groups; however, fusion scores were higher with rhBMP-2 (p = 0.008). Both treatments resulted in significantly reduced segmental ROM (p < 0.001) and greater stiffness (p = 0.009) when compared with non-operated controls; however, the degree of stabilization was significantly higher with rhBMP-2 treatment relative to the HA-DBM scaffold. In the mechanistic studies, PLGA and HA scaffolds were used as negative controls. Both rhBMP-2 and HA-DBM treatments resulted in significant elevations of several osteogenesis-associated genes, including Runx2, Osx, and Alp. The rhBMP-2 treatment led to significantly greater early, mid, and late osteogenic markers, which may be the mechanism in which early clinical complications are seen. The HA-DBM scaffold also induced osteogenic gene expression, but primarily at the 2-week postoperative timepoint. Overall, our findings show promise for this 3D-printed composite as a recombinant growth factor-free bone graft substitute for spinal fusion. STATEMENT OF SIGNIFICANCE: Despite current developments in bone graft technology, there remains a significant void in adequate materials for bone regeneration in clinical applications. Two of the most efficacious bone graft options are the gold-standard iliac crest bone graft and recombinant human-derived bone morphogenetic protein-2 (rhBMP-2), available commercially as Infuse™. Although efficacious, autologous graft is associated with donor-site morbidity, and Infuse™ has known side effects related to its substantial host inflammatory response, possibly associated with a immediate, robust osteoinductive response. Hence, there is a need for a bone graft substitute that provides adequate osteogenesis without associated adverse events. This study represents a significant step in the design of off-the-shelf growth factor-free devices for spine fusion.

Animal and translational models of SARS-CoV-2 infection and COVID-19

COVID-19 is causing a major once-in-a-century global pandemic. The scientific and clinical community is in a race to define and develop effective preventions and treatments. The major features of disease are described but clinical trials have been hampered by competing interests, small scale, lack of defined patient cohorts and defined readouts. What is needed now is head-to-head comparison of existing drugs, testing of safety including in the background of predisposing chronic diseases, and the development of new and targeted preventions and treatments. This is most efficiently achieved using representative animal models of primary infection including in the background of chronic disease with validation of findings in primary human cells and tissues. We explore and discuss the diverse animal, cell and tissue models that are being used and developed and collectively recapitulate many critical aspects of disease manifestation in humans to develop and test new preventions and treatments.

Nanostructured Biomaterials for Bone Regeneration

This review article addresses the various aspects of nano-biomaterials used in or being pursued for the purpose of promoting bone regeneration. In the last decade, significant growth in the fields of polymer sciences, nanotechnology, and biotechnology has resulted in the development of new nano-biomaterials. These are extensively explored as drug delivery carriers and as implantable devices. At the interface of nanomaterials and biological systems, the organic and synthetic worlds have merged over the past two decades, forming a new scientific field incorporating nano-material design for biological applications. For this field to evolve, there is a need to understand the dynamic forces and molecular components that shape these interactions and influence function, while also considering safety. While there is still much to learn about the bio-physicochemical interactions at the interface, we are at a point where pockets of accumulated knowledge can provide a conceptual framework to guide further exploration and inform future product development. This review is intended as a resource for academics, scientists, and physicians working in the field of orthopedics and bone repair.

Tracing the fate of limbal epithelial progenitor cells in the murine cornea

Stem cell (SC) division, deployment, and differentiation are processes that contribute to corneal epithelial renewal. Until now studying the destiny of these cells in a living mammal has not been possible. However, the advent of inducible multicolor genetic tagging and powerful imaging technologies has rendered this achievable in the translucent and readily accessible murine cornea. K14CreER(T2)-Confetti mice that harbor two copies of the Brainbow 2.1 cassette, yielding up to 10 colors from the stochastic recombination of fluorescent proteins, were used to monitor K-14(+) progenitor cell dynamics within the corneal epithelium in live animals. Multicolored columns of cells emerged from the basal limbal epithelium as they expanded and migrated linearly at a rate of 10.8 µm/day toward the central cornea. Moreover, the permanent expression of fluorophores, passed on from progenitor to progeny, assisted in discriminating individual clones as spectrally distinct streaks containing more than 1,000 cells within the illuminated area. The centripetal clonal expansion is suggestive that a single progenitor cell is responsible for maintaining a narrow corridor of corneal epithelial cells. Our data are in agreement with the limbus as the repository for SC as opposed to SC being distributed throughout the central cornea. This is the first report describing stem/progenitor cell fate determination in the murine cornea using multicolor genetic tracing. This model represents a powerful new resource to monitor SC kinetics and fate choice under homeostatic conditions, and may assist in assessing clonal evolution during corneal development, aging, wound-healing, disease, and following transplantation.

5-HT1A Receptor-Mediated Autoinhibition and the Control of Serotonergic Cell Firing

The idea that serotonergic synaptic transmission plays an essential role in the control of mood and the pharmacotherapy of anxiety and depression is one of the cornerstones of modern biological psychiatry. As a result, there is intense interest in understanding the mechanisms controlling the activity of serotonin-synthesizing (serotonergic) neurons. One of the oldest and most durable ideas emerging from this work is that serotonergic neurons are capable of autonomously regulating their own basal firing rate. Serotonergic neurons express on their surface 5-HT1A receptors (autoreceptors) that, when activated, induce the opening of potassium channels that hyperpolarize and thereby inhibit cell firing. Activity-dependent release of serotonin within serotonergic nuclei is thought to activate these autoreceptors, thus completing an autoinhibitory feedback loop. This concept, which was originally proposed in the 1970s, has proven to be enormously fruitful and has guided the interpretation of a broad range of clinical and preclinical work. Yet, remarkably, electrophysiological studies seeking to directly demonstrate this phenomenon, especially in in vitro brain slices, have produced mixed results. Here, we critically review this work with a focus on electrophysiological studies, which directly assess neuronal activity. We also highlight recent work suggesting that 5-HT1A receptor-mediated autoinhibition may play other roles in the control of firing besides acting as a feedback regulator for the pacemaker-like firing rate of serotonergic neurons.

Advanced glycation end-products (AGEs) and functionality of reverse cholesterol transport in patients with type 2 diabetes and in mouse models

AIMS/HYPOTHESIS

We investigated the contribution of AGEs to the impairment of reverse cholesterol transport (RCT) variables in diabetic individuals and in two animal models of diabetic obesity and of renal impairment.

METHODS

The capacity of plasma and HDL from 26 individuals with moderately controlled type 2 diabetes to support cholesterol efflux was compared with 26 age- and sex-matched individuals without diabetes. We also compared the rates of RCT in vivo in two animal models: db/db mice and mice with chronic renal failure.

RESULTS

Diabetic individuals had characteristic dyslipidaemia and higher levels of plasma AGEs. The capacity of whole plasma, ApoB-depleted plasma and isolated HDL to support cholesterol efflux was greater for diabetic patients compared with controls despite their lower HDL-cholesterol levels. The capacity of plasma to support cholesterol efflux correlated with plasma levels of cholesteryl ester transfer protein and levels of ApoB, but not with levels of AGE. RCT was severely impaired in db/db mice despite elevated HDL-cholesterol levels and no change in AGE concentration, whereas RCT in uraemic mice was unaffected despite elevated AGE levels.

CONCLUSIONS/INTERPRETATION

AGEs are unlikely to contribute significantly to the impairment of RCT in type 2 diabetes.

BRM and BRG1 subunits of the SWI/SNF chromatin remodelling complex are downregulated upon progression of benign skin lesions into invasive tumours

Background  Nonmelanoma skin cancer is caused by exposure to ultraviolet radiation within sunlight. Actinic keratoses (AKs) are benign precursor lesions that can develop into invasive squamous cell carcinoma (SCC). Little is known about the molecular events that lead to human skin cancer progression from benign to invasive. Objectives  To determine novel genes that may be involved in skin cancer progression based on data from an initial microarray screen of human skin cancers. Methods  The SWI/SNF chromatin remodelling ATPase subunit BRM was identified as being downregulated in SCC but not AK compared with normal skin in our microarray screen. Therefore reverse transcription-polymerase chain reaction, gene methylation and protein expression was used to study BRM and its alternative ATPase subunit BRG1 in a range of human skin cancers. Results  We found reduced levels of mRNA coding for BRM but not BRG1 in SCC. BRM mRNA levels in AK were similar to those in normal skin. Deregulation of BRM did not result from hypermethylation of CpG regions in the promoter of these genes. Both BRM and BRG1 protein was reduced by about 10-fold in 100% of SCC and basal cell carcinoma, but not in AK specimens examined. Conclusions  BRM protein may be decreased due to low levels of mRNA, while BRG1 protein loss appears to be post-translational. BRM and BRG1 may be novel tumour suppressor genes for human skin cancer. They appear to be involved after development of benign lesions, and are downregulated during progression towards invasion.

Effects of divergent selection for serum insulin-like growth factor-I concentration on performance, feed efficiency, and ultrasound measures of carcass composition traits in Angus bulls and heifers

Angus bulls and heifers from lines divergently selected for serum IGF-I concentration were used to evaluate the effects of IGF-I selection line on growth performance and feed efficiency in 2 studies. In study 1, bulls (low line, n = 9; high line, n = 8; initial BW = 367.1 +/- 22.9 kg) and heifers (low line, n = 9; high line, n = 13; initial BW = 286.4 +/- 28.6 kg) were adapted to a roughage-based diet (ME = 1.95 Mcal/kg of DM) for 24 d and fed individually for 77 d by using Calan gate feeders. In study 2, bulls (low line, n = 15; high line, n = 12; initial BW = 297.5 +/- 34.4 kg) and heifers (low line, n = 9; high line, n = 20; initial BW = 256.0 +/- 25.1 kg) were adapted to a grain-based diet (ME = 2.85 Mcal/kg of DM) for 32 d and fed individually for 70 d by using Calan gate feeders. Blood samples were collected at weaning and at the start and end of each study, and serum IGF-I concentration was determined. Residual feed intake (RFI) was calculated, within study, as the residual from the linear regression of DMI on midtest BW(0.75), ADG, sex, sex by midtest BW(0.75) and sex by ADG. In study 1, calves from the low IGF-I selection line had similar initial and final BW and ADG, compared with calves from the high IGF-I selection line. In addition, DMI and feed conversion ratio were similar between IGF-I selection lines; however, calves from the low IGF-I selection line tended (P < 0.10) to have lesser RFI than calves from the high IGF-I selection line (-0.26 vs. 0.24 +/- 0.31 kg/d). In study 2, IGF-I selection line had no influence on performance or feed efficiency traits. However, there was a tendency (P = 0.15) for an IGF-I selection line x sex interaction for RFI. Bulls from the low IGF-I selection line had numerically lesser RFI than those from the high IGF-I selection line, whereas in heifers, the IGF-I selection line had no effect on RFI. In studies 1 and 2, weaning and initial IGF-I concentrations were not correlated with either feed conversion ratio or RFI. However, regression analysis revealed a sex x IGF-I concentration interaction for initial IGF-I concentration in study 1 and weaning IGF-I concentration in study 2 such that the regression coefficient was positive for bulls and negative for heifers. These data suggest that genetic selection for postweaning serum IGF-I concentration had a minimal effect on RFI in beef cattle.

The interaction of metal ions and Marimastat with matrix metalloproteinase 9

The effect of a range of metal ions on the ability of Marimastat to inhibit matrix metalloproteinase 9 (MMP-9) was examined in a fluorescence based proteolytic assay. Whilst none of the metals examined significantly affected the inhibitory ability of Marimastat, several metal ions did have a significant effect on MMP-9 activity itself. In the absence of Marimastat, Zn(II) and Fe(II) significantly inhibited MMP-9 activity at metal ion concentrations of 10 and 100 microM, respectively. In both the absence and presence of Marimastat, Cd(II) significantly inhibited MMP-9 at 100 microM. In contrast, 1 mM Co(II) significantly upregulated MMP-9 proteolytic activity.

Decreased matrix degradation in diabetic nephropathy: effects of ACE inhibition on the expression and activities of matrix metalloproteinases

AIMS/HYPOTHESIS

Extracellular matrix accumulation is thought to be involved in the pathogenesis of diabetic nephropathy. Increased matrix synthesis has been well documented but the effects of diabetes on degradative pathways, particularly in the in vivo setting, have not been fully explored. Furthermore, the effect of renoprotective therapies on matrix accumulation through these pathways has not been examined. We investigated the degradative pathway of type IV collagen and the effects of ACE inhibition in experimental diabetic nephropathy.

METHODS

Diabetes was induced in 16 rats by administrating streptozocin; 8 of the diabetic rats were allocated at random to receive the ACE inhibitor perindopril (2 mg/l) in their drinking water and 8 age and weight matched rats served as controls. Gene expression of matrix metalloproteinase ( MMP) and tissue inhibitor of metalloproteinase ( TIMP) was measured by RT-PCR and type IV collagen content by immunohistochemistry. MMP activities were determined by degradation of a radiolabelled substrate and by zymography.

RESULTS

Six months of diabetes was associated with a decrease in mRNA and enzymatic activity of MMP-9 (21 % and 51 % respectively, p < 0.05 vs control) and a 51 % increase in TIMP-1 mRNA ( p < 0.05 vs control). By contrast, MMP-2 mRNA was increased but its activity decreased (43 % and 43 % respectively, p < 0.05 vs control). Total degradative capacity of kidney tissue from diabetic rats was also lower (Control: 48 +/- 7 %, Diabetic: 33 +/- 6 %, p < 0.05). Activation of latent MMPs with amino-phenylmercuric acetate increased matrix degradation by two-fold. However the relative decrease associated with experimental diabetes still remained. All diabetes-associated changes in MMP and TIMP mRNA and activities were attenuated by perindopril treatment in association with reduced type IV collagen accumulation.

CONCLUSIONS/INTERPRETATION

These results indicate that the impairment of matrix degradation contributes to matrix accumulation in diabetic nephropathy and that the beneficial effects of ACE inhibition could in part be mediated by modulation of changes in matrix degradative pathways.

Effects of glucose on matrix metalloproteinase and plasmin activities in mesangial cells: possible role in diabetic nephropathy

Diabetic nephropathy is characterized by an accumulation of mesangium matrix that correlates well with the loss of kidney function. High glucose concentration is known to increase the synthesis of many matrix components. Recently, we have shown that degradation of matrix also decreases in diabetes. The major enzymes responsible for matrix degradation are the matrix metalloproteinases. The physiology of these enzymes is complex and their activity is tightly regulated at many levels. At the transcriptional level matrix metalloproteinase (MMP) expression is increased by protein kinase C (PKC) agonists, and some growth factors. In contrast transforming growth factor (TGF)-beta can decrease MMP expression. Once synthesized, MMPs are secreted as inactive pro-enzymes that are activated by other MMPs or plasmin. To effect this, plasmin must be liberated from plasminogen in the pericellular environment. In turn, activated MMPs can be inhibited by binding to specific inhibitors known as tissue inhibitor of metalloproteinases (TIMP). Cell culture and animal studies have shown that high glucose (HG) decreases expression of MMPs and increases expression of TIMPs. HG can also affect MMP activation by decreasing plasmin availability and reducing expression of a membrane-bound MMP called MT1-MMP. How HG induces these changes remains to be fully elucidated. One possibility is that HG can increase TGF-beta. which may in turn alter MMP promoter activity: this area is currently being studied in our laboratory.

Absolute quantitation of specific mRNAs in cell and tissue samples by comparative PCR

A comparative PCR assay, for the absolute quantitation of specific mRNAs in cell and tissue samples, has been designed to overcome problems with previous techniques. cDNAs made from the RNAs are co-amplified with "competitor" plasmid templates under conditions in which reagents are not limiting at the equivalence point, thereby preventing competition between target and competitor templates and distinguishing the assay from competitive PCR assays. The cDNAs are serially diluted, and competitor templates concentrations are kept constant, rather than vice versa, as occurs in competitive PCR assays. Products from target and competitor templates are resolved by electrophoresis and measured by phosphorescent or fluorescent imagery. Both products are measured to minimize errors in the competitor:target ratio. A synthetic external standard RNA is included in the tissue lysis solution and co-purified with endogenous mRNAs, thereby being subjected to identical losses of yield during subsequent procedures. The determination of the number of copies of external standard cDNA allows inefficiencies of RNA extraction and cDNA synthesis to be taken into account. Standard concentrations of plasmids containing the endogenous target sequences are also measured, so that corrections can be made for discrepancies due to unequal amplification of target and competitor sequences. These corrections, together with the use of an external standard and the PCR conditions chosen, allow for the accurate, specific and sensitive determination of the absolute number of mRNA copies in a sample.

Epithelial cells up-regulate matrix metalloproteinases in cells within the same mammary carcinoma that have undergone an epithelial-mesenchymal transition

A metastatic rat mammary carcinoma cell line, BC1, contains cells that have retained epithelial differentiation characteristics and metaplastic cells that have undergone an epithelial-mesenchymal transition. These two subpopulations cooperate to degrade collagen. We have used novel PCR assays to quantitate, for the first time, absolute levels of the mRNAs encoding matrix metalloproteinases (MMPs) and tissue inhibitors of metalloproteinases (TIMPs) in cell and tumor samples. BC1 tumors expressed high levels of the collagenase-3, TIMP-2, stromelysin-1, and gelatinase B genes and low levels of the stromelysin-2 and TIMP-1 genes. This pattern of expression was repeated in cultures of BC1 and cultures containing mixed clones of epithelial cells and metaplastic cells. In both BC1 and the biclonal cultures, metaplastic cells were the main source of collagenase-3, stromelysin-1 and stromelysin-2, whereas TIMPs were equally distributed and epithelial cells were the main source of gelatinase B. High levels of all four MMP mRNAs in metaplastic cells were dependent on coculture with epithelial cells, suggesting the production of an inducing factor by the epithelial cells. In contrast, gelatinase B mRNA was produced at a high level by epithelial cells in the absence of metaplastic cells. TIMP-2 mRNA was abundant in both subpopulations grown alone and did not change substantially upon coculture. Thus, the interclonal cooperativity to degrade collagen in BC1 cells required the induction of MMPs in metaplastic cells by epithelial cells. Interclonal cooperativity may be important to the progression of neoplastic tumors, a feature of which is phenotypic heterogeneity.

Direct activation and anti-repression functions of GAL4-VP16 use distinct molecular mechanisms

In order to determine whether the molecular mechanisms used for direct activation by GAL4-VP16 are the same as those used for anti-repression, we have employed monoclonal antibodies specific for the VP16 activation domain. In the absence of added repressors, GAL4-VP16 was able to stimulate transcription from a template containing GAL4-binding sites, and the antibodies raised against the VP16 activation domain failed to inhibit this direct activation. GAL4-VP16 also was able to prevent histone H1-mediated repression by a mechanism that was strongly dependent on the presence of specific GAL4-binding elements in the promoter. However, in contrast to the assays conducted in the absence of repressors, the antibodies were strong inhibitors of GAL4-VP16-activated transcription in the presence of histone H1. Thus the binding of the antibodies distinguished between the direct activation and anti-repression functions of GAL4-VP16, indicating that these functions operate through distinct molecular mechanisms. The anti-repression-specific mechanism that is inhibitable by the antibodies acted at an early stage of preinitiation complex formation. Deletions of individual subdomains of the VP16 activation domain demonstrated that there was not a discrete subdomain responsible for the anti-repression function of GAL4-VP16. Thus, the inhibitory effect of the antibodies appeared to be due to the location of the epitope within the activator protein rather than to some inherent biochemical property of that region of the protein that is required specifically for anti-repression. The inhibitory effect of the antibodies also ruled out the possibility that steric exclusion of repressor proteins from the promoter was the sole means of anti-repression by the transcriptional activator.

Anti-integrin antibodies induce type IV collagenase expression in keratinocytes

During wound healing, pericellular proteolysis is thought to be essential for the detachment of keratinocytes from basement membrane and in their migration into the wound bed. We have characterized integrin-type cell adhesion/migration receptors in human mucosal keratinocytes and examined their function in the regulation of type IV collagenase gene expression. Two major integrins of the beta 1 class, alpha 2 beta 1 and alpha 3 beta 1, were found to function as collagen and fibronectin receptors, respectively. Antibodies against beta 1 and alpha 3 integrin subunits were found to stimulate the expression of the 92 kDa type IV collagenase severalfold in a dose-dependent manner. Keratinocytes expressed also the 72 kDa type IV collagenase, the synthesis of which remained, however, unchanged in keratinocytes treated with anti-integrin antibodies. Stimulation of 92 kDa enzyme was found to be caused directly by antibody binding to integrins, since Fab-fragments of anti-beta 1 antibodies alone were able to induce collagenase expression in the absence of secondary, clustering antibodies. Antibodies against alpha 2 beta 1 integrin caused no stimulation. Keratinocytes seeded on different substrata (plastic, collagen, fibronectin, laminin, or vitronectin) showed equal induction of type IV collagenase expression. Expression of 92 kDa type IV collagenase could not be induced by peptides (GRGDS, GRGES), proteins (fibronectin, laminin, fibrinogen, albumin), or antibodies to fibronectin. We suggest that proteolytic processes around keratinocytes can be regulated by extracellular factors signalling through integrin-type receptors.

Interleukin-1 beta and transforming growth factor-alpha/epidermal growth factor induce expression of M(r) 95,000 type IV collagenase/gelatinase and interstitial fibroblast-type collagenase by rat mucosal keratinocytes

Rat mucosal keratinocytes serially propagated under permanently serum-free conditions responded to interleukin (IL)-1 beta/IL-alpha and to transforming growth factor (TGF)-alpha/epidermal growth factor (EGF) (as well as to 12-O-tetradecanoylphorbol-13-acetate (TPA)) by upregulation of M(r) 95,000 gelatinase (MMP-9) (M(r) 95K GL) and fibroblast-type collagenase (MMP-1) (FIB-CL), whereas control cells expressed barely detectable levels of either of these enzymes. The cells secreted 8-10 micrograms/10(6) cells/day (M(r) 95K GL) and 2-3 micrograms/10(6) cells/day (FIB-CL) of enzyme protein for at least 24 h when maximally induced. This level was attained only after a 24-h lag period, and the earliest emergence of enzyme protein in the culture medium required 10-14 h. IL-1 beta was by far the most potent cytokine with maximal effect already at 10(-10) M, whereas IL-1 alpha, TGF-alpha, and EGF required 20-100-fold higher concentrations. Pretreatment of the cells with TPA (10(-7) M) abolished the subsequent response to IL-1 beta, TGF-alpha, and EGF and at the same time resulted in > 90% reduction of cytosolic protein kinase C activity. Surprisingly, staurosporine, a potent kinase inhibitor, not only failed to block growth factor/cytokine responses but itself stimulated expression of the enzymes at a magnitude comparable to TPA. The inducing effect of TGF-alpha/EGF was down-regulated by 70-85% by 10(-7) M dexamethasone. Dexamethasone was less effective in ablating the IL-1 beta response yielding 60% reduction M(r) 95K GL and little or no reduction of FIB-CL. Dexamethasone also failed to block the TPA response.

Transforming growth factor-beta 1 up-regulates type IV collagenase expression in cultured human keratinocytes

During the wound healing process lysis of basement membranes precedes keratinocyte migration into the wound bed. We studied, in vitro, whether this degradation of basement membranes could be regulated by transforming growth factor-beta 1 (TGF-beta 1), which is known to accelerate wound healing in vivo. Transforming growth factor-beta 1 was found to increase the expression of both 92- and 72-kDa type IV collagenases (gelatinases) in cultured human mucosal and dermal keratinocytes. The 92-kDa enzyme predominated in both unstimulated and stimulated cultures. The 92-kDa form was stimulated over 5-fold, and the other form by a factor of 2-3. This increase in the synthesis of type IV collagenases was associated with a marked increase in the mRNA levels of these enzymes as well. The induction of the 92-kDa enzyme was similar in culture medium containing either 0.15 or 1.2 mM calcium chloride. Rat mucosal keratinocytes secreted only 92-kDa type IV collagenase, the secretion of which was not regulated by TGF-beta 1. Also, TGF-beta 1 did not cause any significant induction (maximum about 1.2-fold) of either type IV collagenase in human gingival fibroblasts. The induction levels of both collagenases in human keratinocytes were independent of the type of the extracellular matrix the cells were grown on. However, the basement membrane matrix (Matrigel) activated about half of the 92-kDa type to its 84-kDa active form. The data suggest that TGF-beta 1 has a specific function in up-regulating the expression of type IV collagenases in human keratinocytes, offering a possible explanation of how keratinocytes detach from basement membranes prior to the migration over the wound bed.

Characteristics of a 95-kDa matrix metalloproteinase produced by mammary carcinoma cells

A Mr 95,000 matrix metalloproteinase (MMP) produced by rat mammary carcinoma cells has been isolated and characterized. The MMP was secreted in a proteolytically inactive form that was free from bound tissue inhibitor of metalloproteinases. The enzyme was highly glycosylated as evident from an apparent drop of Mr from 95,000 to 83,000 after treatment with N-glycanase. Rotary shadowing electron micrographs of purified proenzyme preparations revealed a uniform set of ellipsoidal molecules. Treatment of the proenzyme with 1% SDS resulted in generation of catalytic activity and exposed a cryptic unpaired Cys residue. The latent proenzyme may be activated in at least three additional ways: either spontaneously upon storage, by treatment with organomercurials, or by limited proteolysis by trypsin. Each mode of activation yielded a distinct pattern of cleavage of the enzyme. The activated enzyme cleaved gelatin (denatured type I collagen) and native type IV and V collagen at 30-37 degrees C. Noncollagenous proteins including alpha 1-proteinase inhibitor, casein, and fibrinogen also were cleaved. The rat mammary carcinoma cell line that produces the Mr 95,000 MMP is composed of two distinct (epithelial- and myoepithelial-like) cell types. The enzyme is expressed constitutively by the epithelial cells. This suggests that expression of the Mr 95,000 MMP is regulated differently from that of interstitial collagenase, which is produced by the epithelial cells only in response to specific inductive factor(s) from the myoepithelial-like cells. Monoclonal antibodies raised against the purified latent Mr 95,000 form of the enzyme bind specifically to the Mr 95,000 MMP and have been used to localize the enzyme to the Golgi region and cytoplasmic granules of the epithelial cells.

Immunolocalization of collagenase in neoplastic epithelial cells

The distribution of interstitial collagenase in a rat mammary carcinoma model system has been studied by immunocytochemistry. Rabbit antibodies were raised against collagenase from neoplastic epithelial cells which were derived from an anaplastic, invasive, rat mammary carcinoma (BC1). Specificity of the antibodies was determined by Western blot analysis which showed reactivity with the inactive procollagenase from conditioned culture medium of BC1 cells as well as with purified, active BC1 collagenase. Anti-BC1 collagenase antibodies did not recognize BC1 collagenase entrapped by the inhibitor, rat alpha-2-macroglobulin (alpha 2M), or collagenase derived from TPA-stimulated human fibroblasts. Anti-human fibroblast collagenase antibodies did not recognize BC1 collagenase, suggesting that the human-mesenchymal and rat-epithelial enzymes are immunologically distinct molecules. Collagenase was immunolocalized intracellularly in BC1 cells cultured in the presence of monensin. Neither BC1 collagenase, alpha 2M nor enzyme-inhibitor complexes were demonstrated in or around invading tumours by immunostaining of tissue sections of rat mammary carcinomas.

Cellular interactions determining the production of collagenase by a rat mammary carcinoma cell line

The cellular interactions regulating the production of collagenase by a cell line derived from a spontaneously arising rat mammary carcinoma have been studied. The cell line, BC1, was grown permanently under defined serum-free conditions, so that the poorly characterized and variable effects of serum on collagenase expression were avoided. Two stable subpopulations of cells present in BC1 cultures were defined as epithelioid cells ("E-cells") and myoepithelioid cells ("M-cells"). These subpopulations differed in their morphology, pattern of growth and susceptibility to detachment from culture vessels by trypsin. Seven clones of M-cells and 7 clones of E-cells, obtained by the limiting dilution technique, were used to determine the cellular source of collagenase and the interactions which led to its expression. M-cells displayed an absolute dependence on a soluble factor produced by E-cells for their survival in vitro. The presence of both cellular types in culture was necessary for collagenase secretion to occur, E-cells being the major source of enzyme in mixed cultures. A soluble factor produced by M-cells was largely, if not completely, responsible for the induction of collagenase secretion by E-cells. Clones representative of both subpopulations were tumorigenic in syngeneic host animals. These results suggest that the phenotypic diversity which occurs within populations of neoplastic cells may give rise to subpopulations of cells which display a more aggressive phenotype in coexistence than in isolation.

The collagenase produced by neoplastic rat epithelial cells: modulation of secretion, molecular weight characteristics, and purification

The modulation of the production of collagenase by an epithelial cell line derived from a spontaneously arising rat mammary carcinoma has been studied. The cell line, BC1, was grown permanently under defined serum-free conditions, thus avoiding the poorly characterized and variable effects of serum on collagenase production. Piperazine-N,N'-bis-(2-ethanesulfonic acid) (Pipes), retinoic acid and cytochalasin B all stimulated collagenase secretion, while dexamethasone inhibited it and progesterone, prolactin, prostaglandin E2, and estrogen had no effect. This profile of response to exogenous compounds was distinct from that of cells of mesenchymal origin and from human keratinocytes. For the production of large quantities of collagenase, culture medium was supplemented with Pipes (30 mM, pH 6.8), and retinoic acid (1 microM, on alternate feeds). The collagenase secreted by BC1 cells grown under these conditions was latent and had a molecular mass of 59 kDa. Treatment of the 59 kDa form with trypsin or APMA caused a progressive decrease in molecular mass via 54 kDa and 52 kDa intermediates, to a 48 kDa form. This form was purified to electrophoretic homogeneity by heparin-Sepharose, zinc-chelate-Sepharose, and Sephacryl S-200 chromatography. Five milligrams of purified collagenase were recovered per litre of culture medium.

A spectrophotometric collagenase assay

A quantitative collagenase assay using Coomassie blue staining and microtiter spectrophotometry is described. Collagen is gelled and dried onto the bottom of microwells as substrate, washed, incubated with samples, washed again, and then stained. Absorbance at 590 nm increases linearly with increasing amounts of collagen in the range 5-40 micrograms. Bacterial and mammalian collagenases can be detected within 2 h, and 10 ng of bacterial collagenase may be detected in 16 h. For simple screening applications, activity may be detected by eye. The assay is safe, simple, fast, economical, and sensitive.

Rat carcinoma cells in long-term, serum-free culture provide a continuing supply of collagenase

Neoplastic, epithelial cells derived from a spontaneously-arising rat mammary carcinoma have been cultured in a defined medium, in the absence of serum, continuously, for over 2 years. The medium is a mixture of Ham's F12 and Dulbecco's Modified Eagle's media supplemented with insulin, transferrin and bovine serum albumin. The cells have retained their potential to produce tumours and, in culture, a true vertebrate collagenase. This system provides a continuing supply of vertebrate collagenase through the application of recently developed methods.