Long-Term Ultrasound Twinkling Detectability and Safety of a Polymethyl Methacrylate Soft Tissue Marker Compared to Conventional Breast Biopsy Markers-A Preclinical Study in a Porcine Model

OBJECTIVE

We have studied the use of polymethyl methacrylate (PMMA) as an alternative biopsy marker that is readily detectable with ultrasound Doppler twinkling in cases of in vitro, ex vivo, or limited duration in vivo settings. This study investigates the long-term safety and ultrasound Doppler twinkling detectability of a PMMA breast biopsy marker following local perturbations and different dwell times in a 6-mo animal experiment.

METHODS

This study, which was approved by our Institutional Animal Care and Use Committee, involved three pigs and utilized various markers, including PMMA (Zimmer Biomet), 3D-printed, and Tumark Q markers. Markers were implanted at different times for each pig. Mesh material or ethanol was used to induce a local inflammatory reaction near certain markers. A semiquantitative twinkling score assessed twinkling for actionable localization during monthly ultrasounds. At the primary endpoint, ultrasound-guided localization of lymph nodes with detectable markers was performed. Following surgical resection of the localized nodes, histomorphometric analysis was conducted to evaluate for tissue ingrowth and the formation of a tissue rind around the markers.

RESULTS

No adverse events occurred. Twinkling scores of all markers for all three pigs decreased gradually over time. The Q marker exhibited the highest mean twinkling score followed by the PMMA marker, PMMA with mesh, and Q with ethanol. The 3D-printed marker with mesh and PMMA with ethanol had the lowest scores. All wire-localized lymph nodes were successfully resected. Despite varying percentages of tissue rind around the markers and a significant reduction in overall twinkling (p < 0.001) over time, mean PMMA twinkling scores remained clinically actionable at 6 and 5 mo using a General Electric C1-6 probe and 9L-probe, respectively.

CONCLUSIONS

In this porcine model, the PMMA marker demonstrates an acceptable safety profile. Clinically actionable twinkling aids PMMA marker detection even after 6 mo of dwell time in porcine lymph nodes. The Q marker maintained the greatest twinkling over time compared to all the other markers studied.

Establishment of an in vivo turkey model for the study of flexor tendon repair

Flexor tendon injuries are common and pose a clinical challenge for functional restoration. The purpose of our study was to assess the adequacy of the turkey as a large animal model for flexor tendon injuries in vivo. Twenty-four male turkeys underwent surgical flexor tendon cut and repair. Turkeys were allocated to five groups postoperatively: (1) foot casted in extension and sacrificed after 3 weeks; (2) foot casted in extension and sacrificed after 6 weeks; (3) foot casted in flexion and sacrificed after 3 weeks; (4) foot casted in flexion and sacrificed after 6 weeks; and (5) foot casted in flexion for 6 weeks and then free roaming allowed for an additional 3 weeks before sacrifice. After sacrifice, digits were collected and analyzed for adhesion formation, healing at the macrolevel and histologically, and biomechanical properties-including friction, work of flexion, stiffness, and strength of repair. All turkeys survived anesthesia and surgery. Tendon rupture occurred in all extension casts and in 11% of those casted in flexion. Friction and work of flexion were significantly higher in the repaired digit than the control digit. There was a correlation between duration of immobilization and repair strength. Histologically, the tendon healed with tenocytes migrating into the gap and producing collagen fibers. We have, for the first time, studied flexor tendon injury and repair using turkeys in terms of anesthesia, surgical procedures, postoperative care, and animal husbandry. The findings regarding functional and histological results from this novel avian model were comparable to the most commonly used mammal model. © 2018 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 36:2497-2505, 2018.

Endotracheal Intubation of Rabbits Using a Polypropylene Guide Catheter

Endotracheal intubation in rabbits can be challenging due to their unusual anatomy. Achieving a patent airway during anesthesia is critical for the avoidance of airway obstruction, prevention of gastric tympany, and to allow ventilatory support. Due to the difficulty of intubation, alternative methods such as the use of laryngeal mask airways or laryngeal tubes have been explored. However, these methods do not result in direct access to the trachea and thus may present a risk for development of complications. In addition, lack of direct intubation of the trachea can result in personnel exposure to waste anesthetic gases. Numerous methods for endotracheal intubation have been described, including blind placement, use of a fiberoptic laryngoscope or endoscope, and cricoid placement. Despite these numerous publications, many still struggle to achieve success. Here we provide a detailed description of an intubation technique that can be taught with minimal training with a short time to proficiency. Briefly, after administration of injectable anesthesia and proper positioning of the rabbit, a polypropylene catheter is placed into the trachea by direct visualization using a laryngoscope. The catheter is then used as a guide to direct the endotracheal tube into the trachea. This method allows for intubation without the need for expensive equipment and can be performed by a single individual without the need for an assistant. In conclusion, this technique can be easily taught and performed at very little cost in any clinical or research setting.

Swine model for translational research of invasive intracranial monitoring

Focal cortical epilepsy is currently studied most effectively in humans. However, improvement in cortical monitoring and investigational device development is limited by lack of an animal model that mimics human acute focal cortical epileptiform activity under epilepsy surgery conditions. Therefore, we assessed the swine model for translational epilepsy research. Swine were used due to their cost-effectiveness, convoluted cortex, and comparative anatomy. The anatomy has all the same brain structures as the human, and in similar locations. Focal subcortical injection of benzyl-penicillin produced clinical seizures correlating with epileptiform activity demonstrating temporal and spatial progression. Swine were evaluated under five different anesthesia regimens. Of the five regimens, conditions similar to human intraoperative anesthesia, including continuous fentanyl with low dose isoflorane, was the most effective for eliciting complex, epileptiform activity after benzyl-penicillin injection. The most complex epileptiform activity (spikes, and high frequency activity) was then repeated reliably in nine animals, utilizing 14 swine total. There were 20.1 ± 10.8 [95% confidence interval (CI) 11.8-28.4] epileptiform events with > 3.5 Hz activity occurring per animal. Average duration of each event was 46.3 ± 15.6 (95% CI 44.0-48.6) s, ranging from 20-100 s. In conclusion, the acute swine model of focal cortical epilepsy surgery provides an animal model that mimics human surgical conditions with a large brain and gyrated cortex, and is relatively inexpensive among animal models. Therefore, we feel this model provides a valuable, reliable, and novel platform for translational studies of implantable hardware for intracranial monitoring.

Safety studies on intrahepatic or intratumoral injection of oncolytic vesicular stomatitis virus expressing interferon-beta in rodents and nonhuman primates

Toxicology studies were performed in rats and rhesus macaques to establish a safe starting dose for intratumoral injection of an oncolytic vesicular stomatitis virus expressing human interferon-beta (VSV-hIFNbeta) in patients with hepatocellular carcinoma (HCC). No adverse events were observed after administration of 7.59 x 10(9) TCID(50) (50% tissue culture infective dose) of VSV-hIFNbeta into the left lateral hepatic lobe of Harlan Sprague Dawley rats. Plasma alanine aminotransferase and alkaline phosphatase levels increased and platelet counts decreased in the virus-treated animals on days 1 and 2 but returned to pretreatment levels by day 4. VSV-hIFNbeta was also injected into normal livers or an intrahepatic McA-RH7777 HCC xenograft established in Buffalo rats. Buffalo rats were more sensitive to neurotoxic effects of VSV; the no observable adverse event level (NOAEL) of VSV-hIFNbeta in Buffalo rats was 10(7) TCID(50). Higher doses were associated with fatal neurotoxicity and infectious virus was recovered from tumor and brain. Compared with VSV-hIFNbeta, toxicity of VSV-rIFNbeta (recombinant VSV expressing rat IFN-beta) was greatly diminished in Buffalo rats (NOAEL, >10(10) TCID(50)). Two groups of two adult male rhesus macaques received 10(9) or 10(10) TCID(50) of VSV-hIFNbeta injected directly into the left hepatic lobe under computed tomographic guidance. No neurological signs were observed at any time point. No abnormalities (hematology, clinical chemistry, body weights, behavior) were seen and all macaques developed neutralizing anti-VSV antibodies. Plasma interleukin-6, tumor necrosis factor-alpha, and hIFN-beta remained below detection levels by ELISA. On the basis of these studies, we will be proposing a cautious approach to dose escalation in a phase I clinical trial among patients with HCC.

Aging is associated with impaired thrombus resolution in a mouse model of stasis induced thrombosis

INTRODUCTION

To evaluate the effects of aging on venous thrombosis.

MATERIAL AND METHODS

Anesthetized male mice (C57BL/6, n=125) underwent complete inferior vena cava occlusion to produce venous thrombosis. Experimental groups included 11-month-old mice (OLD), 2-month-old mice (YOUNG), and age-matched non-thrombosed controls. Mice were euthanized and the following parameters were evaluated two days post-thrombosis: thrombus mass (grams/cm), vein wall inflammatory cells (cells per 5 high powered fields), active plasma plasminogen activator inhibitor-1 (PAI-1, ng/mL), vein wall P-selectin protein determination by ELISA (pg/mL), circulating plasma microparticles (MPs, MPs/200microL), MP tissue factor (TF) activity (pM), and in vivo MP re-injection experiments.

RESULTS

Thrombosed OLD mice had greater thrombus mass than YOUNG mice (389+/-18 vs. 336+/-14 gx10(-4)/cm, P<.05). OLD mice had decreased vein wall monocyte, lymphocyte, and total inflammatory cell populations versus YOUNG mice (P<.05). Vein wall P-selectin levels were greater in OLD thrombosed mice versus YOUNG (7306+/-938 vs. 3805+/-745pg/mL, P<.05). Active plasma PAI-1 concentrations were increased in OLD mice versus YOUNG thrombosed animals (20+/-4 vs. 8+/-2ng/mL, P<.05). OLD mice had significantly higher circulating leukocyte-derived MPs versus YOUNG mice (5817+/-850 vs. 2563+/-283 MPs/200muL PPP, P<.01). OLD mice had plasma MPs with increased TF activity versus YOUNG animals post-thrombosis (34+/-4 vs. 24+/-2 pM, P<.05). Finally, YOUNG recipient animals, whether re-injected with OLD or YOUNG donor MPs, had a significant increase in thrombus mass versus OLD recipient animals (P<.01).

CONCLUSION

Aging influenced several circulating and vein wall factors that decreased thrombus resolution in older animals compared to younger ones in our mouse thrombosis model.

Prophylactic P-selectin inhibition with PSI-421 promotes resolution of venous thrombosis without anticoagulation

P-selectin inhibition has been evaluated as a therapeutic for prevention and treatment of venous thrombosis. In this study, a novel oral small-molecule inhibitor of P-selectin, PSI-421, was evaluated in a baboon model of stasis induced deep vein thrombosis (DVT). Experimental groups included i) primates receiving a single oral dose of 1 mg/kg PSI-421 two days prior and continued six days after thrombosis (n = 3); ii) primates receiving a single daily subcutaneous dose of 0.57 mg/kg enoxaparin sodium two days prior and continued six days post thrombosis (n = 3); and iii) primates receiving no treatment (n = 3). PSI-421 treated primates had greater percent vein reopening and less vein wall inflammation than the enoxaparin and controls at day 6. Microparticle tissue factor activity (MPTFA) was significantly lower in the animals receiving PSI-421 immediately after thrombosis (T+6 hours day 0) suggesting lower potential for thrombogenesis in these animals. PSI-421 also reduced soluble P-selectin levels versus controls at T+6 hours day 0, day 2 and 6. Experimental animals in any group showed no adverse effects on coagulation. This study is the first to demonstrate a reduction in MPTFA associated with vein reopening and reduced vein inflammation due to oral P-selectin inhibition in a baboon model of DVT.

Quantification, distribution, and possible source of bacterial biofilm in mouse automated watering systems

The use of automated watering systems for providing drinking water to rodents has become commonplace in the research setting. Little is known regarding bacterial biofilm growth within the water piping attached to the racks (manifolds). The purposes of this project were to determine whether the mouse oral flora contributed to the aerobic bacterial component of the rack biofilm, quantify bacterial growth in rack manifolds over 6 mo, assess our rack sanitation practices, and quantify bacterial biofilm development within sections of the manifold. By using standard methods of bacterial identification, the aerobic oral flora of 8 strains and stocks of mice were determined on their arrival at our animal facility. Ten rack manifolds were sampled before, during, and after sanitation and monthly for 6 mo. Manifolds were evaluated for aerobic bacterial growth by culture on R2A and trypticase soy agar, in addition to bacterial ATP quantification by bioluminescence. In addition, 6 racks were sampled at 32 accessible sites for evaluation of biofilm distribution within the watering manifold. The identified aerobic bacteria in the oral flora were inconsistent with the bacteria from the manifold, suggesting that the mice do not contribute to the biofilm bacteria. Bacterial growth in manifolds increased while they were in service, with exponential growth of the biofilm from months 3 to 6 and a significant decrease after sanitization. Bacterial biofilm distribution was not significantly different across location quartiles of the rack manifold, but bacterial levels differed between the shelf pipe and connecting elbow pipes.

Gangrenous Clostridium perfringens infection and subsequent wound management in a rhesus macaque (Macaca mulatta)

A 10-y-old female rhesus macaque presented acutely with 3 large (diameter, greater than 4 cm), malodorous, ulcerogangrenous skin wounds on the left caudal thigh and calf. Limb radiographs revealed free gas infiltrating deep tissues, and histologic examination confirmed myonecrosis. Clostridium perfringens, Staphylococcus aureus, and Prevotella intermedia were isolated from the wounds. Antimicrobials, analgesics, and aggressive debridement of necrotic skin and muscle resulted in immediate clinical improvement of the primate. At 1 wk prior to presentation, the animal had received several intramuscular injections in close proximity to the site of infection. Repeated intramuscular injections through excrement-contaminated skin possibly contributed to the pathogenesis of infection. Continued therapy consisted of biweekly wound debridement and nonadherent bandage changes for 7 wk. The macaque regained full use of the affected leg and remains in good physical condition at our facility. Our management of this case led to improvements in training regarding intramuscular injection practices in our macaque colony. This case study is the first report of Clostridium perfringens myonecrosis in a laboratory nonhuman primate. We discuss various methodologies for the diagnosis and treatment of necrotizing clostridial infections.

Resolution of venous thrombosis using a novel oral small-molecule inhibitor of P-selectin (PSI-697) without anticoagulation

P-selectin inhibition has been shown to decrease thrombogenesis in multiple animal species. In this study, we show that a novel oral small-molecule inhibitor of P-selectin, PSI-697, promotes thrombus resolution and decreases inflammation in a baboon model of venous thrombosis. Experimental groups consisted of the following: 1) primates receiving a single oral dose of PSI-697 (30 mg/kg) daily starting three days pre-iliac vein balloon occlusion, and continued for six days; 2) primates receiving a single treatment dose of a low-molecular-weight-heparin (LMWH) (1.5 mg/kg) daily starting one day pre-iliac balloon occlusion, and continued for six days; and 3) primates receiving a single oral dose of a vehicle control daily starting three days pre-iliac vein balloon occlusion, and continued for six days. Animals receiving PSI-697, although thrombosed after balloon deflation, demonstrated greater than 80% vein lumen opening over time, with no opening (0%) for vehicle control (p < 0.01). LMWH opening evident after balloon deflation slightly deteriorated over time compared to PSI-697. PSI-697 therapy also significantly decreased vein wall inflammation determined by magnetic resonance venography (MRV). Importantly, this beneficial opening occurred without measured anticoagulation. Animals receiving PSI-697 demonstrated significantly increased plasma D-dimer levels versus LMWH and control animals six hours post thrombus induction (p < 0.01). This study is the first to demonstrate the effectiveness of oral P-selectin inhibition to modify venous thrombogenesis, increase vein lumen opening, and decrease inflammation in a large animal model.

Treatment with an oral small molecule inhibitor of P selectin (PSI-697) decreases vein wall injury in a rat stenosis model of venous thrombosis

BACKGROUND

Vein wall injury after thrombosis is multifactorial but seems dependent on thrombus and local thrombotic and inflammatory mechanisms. We hypothesized that inhibition of vein wall injury through reduction of thrombotic and inflammatory events with P-selectin inhibition and/or low-molecular-weight heparin (LMWH) occurs independently of thrombus resolution in a rat model of venous thrombosis.

METHODS

Male rats underwent inferior vena cava (IVC) stenosis (94.4% +/- 0.5% reduction in IVC diameter) to induce thrombosis. Rats were treated from 2 days after thrombosis until they were killed 7 days later. Groups consisted of (1) PSI-697, a P-selectin inhibitor (30 mg/kg; oral gavage daily); (2) LMWH-Lovenox (LOV; enoxaparin) 3 mg/kg subcutaneously daily; (3) PSI-697 (30 mg/kg; oral gavage daily) plus LOV 3 mg/kg subcutaneously daily (PSI + LOV); (4) and untreated controls. Evaluations included thrombus mass, vein wall tensiometry (stiffness [inverse of compliance]), intimal thickness scoring by light microscopy, vein wall inflammatory mediators by enzyme-linked immunosorbent assay, and vein wall inflammatory cells by histologic evaluation.

RESULTS

Thrombus mass was not reduced by any treatment. Animals treated with PSI-697 alone, LOV alone, or PSI + LOV demonstrated significant decreases in vein wall stiffness when compared with controls. The vein wall stiffness of the PSI-697-treated groups was also significantly lower than in the LOV-only group. Animals treated with PSI-697 showed a significantly decreased intimal thickness score when compared with vehicle control IVCs. Vein wall intimal thickening was also significantly decreased in animals treated with PSI-697 vs LOV. The PSI-697 and PSI + LOV groups manifested significant decreases in the immunoregulatory and inflammatory cytokine interleukin 13 as compared with controls and LOV. Vein wall monocyte chemotactic protein 1 levels were also significantly reduced in the PSI-697 and PSI + LOV groups vs control. Only PSI-697 significantly decreased vein wall levels of platelet-derived growth factor betabeta. Both the LOV and PSI + LOV groups had significant increases in vein wall monocytes and total inflammatory cells vs controls.

CONCLUSIONS

These data suggest that both LMWH and PSI-697 inhibit vein wall injury independently of thrombus mass. P-selectin inhibition seemed superior to LMWH in measured parameters of injury and mediator inhibition.