United States

Background
Diabetic retinopathy (DR) is a serious diabetes complication that affects millions worldwide. Current therapies are invasive and only slow late-stage progression, thus the development of less invasive, novel therapies that attenuate progression are paramount. In the diabetic milieu, inducible nitric oxide synthase (iNOS) expression is upregulated in retinal macrophages/microglia, which increases production of inflammatory cytokines and reactive oxygen species, worsening ischemia, blood-retinal-barrier (BRB) compromise, and disease progression. Arginase 1 (Arg1) is a ureohydrolase that competes with iNOS for their common substrate, L-arginine. Recent studies revealed a neuroprotective role of Arg1 in murine models of retinal ischemia/reperfusion injury and ischemic stroke and demonstrated the beneficial effects of Arg1 administration in these models. As DR also involves ischemia and inflammation, we hypothesized that exogenous Arg1 would be similarly beneficial through iNOS substrate depletion, resulting in decreased retinal inflammation and oxidative stress.

Methods
Using the obese, type 2 diabetic db/db mouse model that well-approximates human DR pathophysiology, the visual function, BRB, retinal inflammation, and oxidative stress were characterized in these mice aged 16-24-weeks and compared to lean, littermate controls. Visual function was determined by electroretinography (ERG) responses, visual acuity, and contrast threshold measurements. Retinas were collected for immunofluorescence or western blot analyses for iNOS, inflammatory cytokines (IL-1β, TNF-α), oxidative stress (3-nitrotyrosine, 4-hydroxynonenal), and BRB assessment, determined by both retinal albumin extravasation and co-labeling for ZO-1 (tight junction protein) and CD31 (endothelial cell-specific protein). To assess Arg1 therapeutic potential, recombinant Arg1 conjugated to polyethylene glycol (PEG-Arg1), for improved half-life, or a PEG-5000 vehicle control was administered intraperitoneally (25mg/kg) to 16-24-week-old db/db mice thrice weekly for 2 weeks and the same experiments were performed.

Results
Compared to lean littermate controls, db/db mice exhibited significant visual dysfunction, BRB compromise, and elevated retinal levels of iNOS, IL-1β, TNF-α, 3-nitrotyrosine, and 4-hydroxynonenal. PEG-Arg1 treatment significantly ameliorated visual function impairment and BRB compromise in these mice and markedly reduced iNOS levels, retinal inflammation, and oxidative stress compared to vehicle-treated db/db mice. 

Conclusion
The retinal pathology of db/db mice significantly improved with PEG-Arg1 therapy. Though further investigation is necessary, these results suggest that systemic PEG-Arg1 administration has potential as a novel DR therapeutic.

AMA Research Challenge 2022

Systemic Administration of Pegylated Arginase-1 Attenuates Progression of Diabetic Retinopathy in the db/db Mouse

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#### Event Details
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Ricardo Correa, MD, EdD
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Jessica Li, MD/PhD Candidate
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Charles Lopresto, DO

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Welcome to the largest national, multi-specialty research event featuring research from 750 medical students, residents and fellows, and international medical graduates.


poster

Background
Superior Capsule Reconstruction (SCR) allows for the repair of irreparable rotator cuff tears in the younger active patient population. While the use of various graft materials has been described, the choice of using an autograft versus an allograft currently remains unclear. This study aimed to biomechanically investigate SCR with the use of a long head of the biceps tendon (LHBT) autograft and human dermal (HD) allograft in regard to functional abduction force and superior translation of the humeral head. 

Methods
8 fresh-frozen cadaveric shoulder specimens were tested in 5 conditions: (1) intact, (2) complete supraspinatus tear, (3) LHBT autograft, (4) LHBT autograft with side-to-side suturing, and (5) HD allograft with side-to-side suturing. Functional abduction force, superior translation of the humeral head, translational range of motion, and rotational range of motion were tested at 0º, 30º, 60º, and 90º of abduction within each condition. Data was analyzed using analysis of variance with post-hoc Tukey testing for pairwise comparison, with a significance value set at 0.05.

Results
Functional abduction force in the LHBT, LHBT+ suture, and HD+ suture conditions was significantly increased compared to the supraspinatus tear condition at abduction angles of 30º (p=0.011, 0.001, and 0.017 respectively), 60º (p=0.004, 0.001, and 0.002 respectively), and 90º (p=0.013, 0.001, and 0.038 respectively). Additionally, superior translation of the humeral head in the LHBT, LHBT+ suture, and HD+ suture conditions was significantly decreased compared to the tear condition at abduction angles of 30º (p=0.03, 0.049, 0.03 respectively) and 60º (p=0.02, 0.04, 0.03 respectively). All 3 reconstructive techniques were statistically identical to the intact rotator cuff condition in regard to translational and rotational range of motion.

Conclusion
SCR with LHBT autograft without side-to-side suturing, LHBT with posterior side-to-side suturing, and HD allograft with posterior side-to-side suturing all equivalently restore functional abduction force and decrease superior translation of the humeral head after a complete supraspinatus tear. Additionally, all three reconstructive techniques display no deficits in both translational and rotational range of motion, resembling the intact rotator cuff state.


Orthopaedic Surgery - Biceps Autograft versus Dermal Allograft for Superior Capsule Reconstruction after Rotator Cuff Tear - Orthopaedic Surgery

Orthopaedic Surgery - Changes to Excursion of Rotator Cuff Muscles during Abduction after Superior Capsular Reconstruction (SCR) and Reverse Total Shoulder Arthroplasty (rTSA) - Orthopaedic Surgery

Background
Volumetric muscle loss (VML) is a traumatic or surgical orthopaedic injury characterized by a significant loss of skeletal muscle mass and function. Clinically there is no treatment that targets skeletal muscle after VML, and lifelong functional impairments lead to musculoskeletal deformity and comorbidities. While mechanisms driving chronic lack of regeneration remain unclear, pathologic fibrotic deposition and loss of myogenic signaling after injury are thought to be involved. One near-term solution to improve function following VML is to repurpose FDA-approved drugs. This study’s objective was to evaluate effectiveness of an anti-fibrotic, nintedanib, and a hypertrophy stimulant, formoterol combined with leucine, to improve muscle function and regeneration after VML. Muscle function after VML is the key clinical outcome; evaluation of torque thus serves as the main measure of success.

Methods
Adult (12-week-old) male C57BL/6 mice (n=29) underwent unilateral VML surgery removing ~15% of the posterior muscle compartment (gastrocnemius, soleus, plantaris) or remained injury-naïve controls. VML-injured mice were randomized to nintedanib (6mg/kg/day), formoterol (3mg/kg/day) and leucine (24g/kg/day), or no treatment. Six weeks post-VML activity and whole-body metabolism were evaluated. Maximal in vivo muscle torque was evaluated 8 weeks post-VML, and tissue was collected terminally. Data were evaluated using a one-way ANOVA and Tukey post-hoc, with significance at p<0.05.

Results
Twenty-four-hour metabolic rate was ~17% and 8% higher in the formoterol+leucine group (16.5kcal/hour) compared to injury naïve and VML alone, respectively (p<0.001); despite no ambulation or respiratory exchange ratio differences (p≥0.069). However, formoterol+leucine treatment increased lipid oxidation (p=0.005). After 8-weeks, gastrocnemius mass:body mass was reduced for VML alone, but both treatments ameliorated this difference (p=0.004). Maximal in vivo torque was greatest in injury naïve mice (609.6mN•m/kg) and ~41% and 49% lower in VML untreated and nintedanib groups, respectively, while formoterol+leucine mitigated this decline (p=0.012).

Conclusion
Understanding the effects of repurposed FDA-approved medications on functional recovery after VML can establish translational options. Formoterol+leucine treatment improved torque of the posterior muscle compartment and muscle mass to a level not statistically different from injury-naïve mice, supporting its role in promoting functional recovery after VML. This strategy warrants further research to consider applications for VML-injured patients.

Orthopaedic Surgery - Drug Therapies after Volumetric Muscle Loss Injury: Recovery of Function and Muscle Mass with Formoterol - Orthopaedic Surgery

Orthopaedic Surgery - Effects of different 3D-printed titanium surfaces on cell behaviors in vitro - Orthopaedic Surgery

Orthopaedic Surgery - Fibro-adipogenic Progenitors (FAPs) in Heart, Diaphragm and Muscle in a Novel PDGFRa-reporter Duchenne’s Muscular Dystrophy (DMD) Mouse Model - Orthopaedic Surgery

Background:
There is a strong desire in orthopaedics to have soft tissue, particularly tendon, grow into metallic implants. Extensor mechanism and abductor reconstructions in total joint arthroplasty are problematic, and current methods for repair are associated with substantial complications and failure rates. With the introduction of three-dimensional (3D) printed porous metal implants, we hypothesized that tendons could directly attach to the implants. However, the effects of the porous metal structure on tissue growth and penetration into the pores are unknown. In order to improve outcomes after tendon injury, a better understanding of the optimal conditions to promote healing and prevent fibrosis is needed. Using a rat model, we investigated the effect of pore size on tendon repair fixation using 3D printed titanium implants.

Methods:
There were three experimental groups of eight Sprague Dawley rats (n = 24) plus control (n = 3). Implants had defined pore sizes of 400μm (n = 8), 700μm (n = 8), and 1000μm (n = 8). A defect was created in the Achilles tendon and the implant positioned between cut ends and secured with suture. Specimens were harvested at twelve weeks. Half the specimens underwent mechanical testing to assess tensile load to failure. The remaining specimens were fixed and processed for hard tissue histological analysis.

Results:
The average load to failure was 72.6N for controls (SD 10.04), 29.95N for 400μm (SD 17.95), 55.08N for 700μm (SD 13.47), and 63.08N for 1000μm (SD 1.87). The load to failure was generally better in the larger pore sizes. The 700m and 1000m specimens performed similarly, while the 400m showed significant differences vs control (p = 0.039), vs 1000μm (p = 0.010), and approached significance vs 700μm (p = 0.066). There was increasing ingrowth as pore sized increased. Histology showed fibrous tendon tissue within and around the implants, with collagen fibers organized in bundles.

Conclusion:
Tendon repair utilizing implants with 700μm and 1000μm pores exhibited similar load to failure as controls. Using a defined pore structure at the attachment points of tendons to implants may allow predictable tendon ingrowth onto/into an implant at the time of revision arthroplasty.

Orthopaedic Surgery - Influence of Porosities of Titanium Implants on Tensile Properties in a Rat Tendon Repair Model - Orthopaedic Surgery

Background
Postoperative complications are a concern for surgeons due to worse outcomes and increased cost. It has been shown that social determinants of health disparities (SDHD) are associated with higher rates of postoperative complications. Understanding the role SDHD plays in patient’s health can help prepare providers to optimize patients’ conditions prior to surgery and improve postoperative care. The purpose of this study was to compare the postoperative complication rates between patients undergoing total shoulder arthroplasty (TSA) with a past medical history of SDHD with a control group without SDHD diagnoses.
Methods
A retrospective cohort analysis was conducted using a national insurance claims database. Using International Classification of Diseases (ICD) and Current Procedural Terminology (CPT) codes patients who underwent primary TSA with at least two years of follow-up in the database were identified. The SDHD and control groups were matched and analyzed using multivariable analysis for 90-day medical complications and 2-year surgical complications.
Results
A total of 120,367 patients underwent TSA between 2010-2019: 110,822 patients in control group and 9,394 in SDHD group. SDHD group had significantly longer length of stay (mean [SD]; Control = 1.99 days [1.39] vs SDHD = 3.84 days [18.32]; p<0.001) along with significantly higher odds ratios for 90-day medical complications including heart failure (OR: 3.71; p<0.001), cerebrovascular accident (OR: 2.48; p<0.001), renal failure (OR: 2.91; p<0.001), death (OR: 3.32; p<0.001), deep vein thrombosis (OR: 3.16; p<0.001), pulmonary embolism (OR: 1.95; p<0.001), pneumonia (OR: 2.84; p<0.001), sepsis (OR: 4.94; p<0.001), and urinary tract infection (OR: 2.60; p<0.001). Additionally, the SDHD group had a significantly higher odds ratio for revision surgery within 2-years following TSA (OR: 1.45; p<0.001).
Conclusion
This study highlights the negative impact of SDHD on patient outcomes following TSA including a higher rate of postoperative complications within 90-days and revision surgery within 2-years. Additionally, patients with a history of SDHD had a significantly longer length of hospital stay than patients without SDHD. Quantifying the risk of complications and differences in length of stay for TSA patients with a history of SDHD are important in determining value-based payment models and risk stratification to optimize patient care.

Orthopaedic Surgery - Social Determinants of Health Disparities Impact Postoperative Complications in Patients Undergoing Total Shoulder Arthroplasty - Orthopaedic Surgery

Background
Neurofibromatosis type 2 (NF2) is an autosomal dominant tumor predisposition syndrome resulting from mutations in the NF2 gene. NF2 patients are prone to developing schwannomas, which are benign tumors originating from Schwann cells of the peripheral nervous system. Though the hallmark of NF2 is the development of bilateral vestibular schwannomas, schwannomas can occur on any cranial or peripheral nerve. Facial nerve schwannoma (FNS) is the most common primary neoplasm of the facial nerve, although it is uncommon overall. Due to the rarity of FNS, animal models are imperative for therapeutic testing of pharmaceutical compounds. The Postn-Cre;Nf2flox/flox mouse model is known to develop cranial nerve schwannomas, including FNS. However, the nature of these tumors has not been robustly characterized.

Methods
Postn-Cre;Nf2flox/flox and control littermates were euthanized at 12 months of age. A novel method was employed for dissection of the intratemporal facial nerve. Whole heads or isolated facial nerves were formalin-fixed and paraffin embedded. Sections were stained by hematoxylin and eosin or immunohistochemistry. Schwann cell density and tumorlets were quantified in geniculate ganglia and peri-geniculate facial nerves. Comparative statistical analysis was performed using Student’s t-test (GraphPad Prism).

Results
In this study, we report the first thorough histopathological analysis of FNS development in the Postn-Cre;Nf2flox/flox mouse model. Schwann cell density is increased in mutant facial nerves and geniculate ganglia compared to control (p<0.001). Tumorlets are present only in Postn- Cre;Nf2flox/flox mutant mouse ganglia (p<0.01). Neuron density is decreased in mutant geniculate ganglia (p<0.001). Merlin, S100, SOX10, GFAP, FABP7, Neurofilament, and Ki-67 immunostaining confirmed a Schwann cell phenotype.

Conclusion
The Postn-Cre;Nf2flox/flox mouse model demonstrates consistent and predictable development of facial nerve schwannoma. While this model has been described to develop cranial nerve schwannomas, our study establishes the first quantifiable readout of tumor burden through measurement of Schwann cell and tumorlet density. These findings provide a novel endpoint for preclinical testing of targeted therapies for neurofibromatosis type 2-associated cranial nerve schwannomas in the Postn-Cre;Nf2flox/flox mouse model.

Facial Nerve Schwannoma Development in a Genetically Engineered Neurofibromatosis Type 2Mouse Model

Abstract Title:
Pancreatic Lipase Deficiency: Characterization of Novel PNLIP Mutations

Background:
Pancreatic triglyceride lipase (PNLIP) is the primary lipase responsible for dietary fat digestion in humans. Studies have reported that mutations in PNLIP lead to pancreatic lipase deficiency, steatorrhea, and fat-soluble vitamin deficiencies. Previously, we illustrated that a rare homozygous missense mutation (p.T221M) in PNLIP causes steatorrhea through its secretion defect. This led to a loss of digestive lipase function, insoluble aggregation via protein misfolding, and a gain of proteotoxic function increasing the risk for pancreatic diseases like pancreatitis. Recently, two more novel PNLIP mutations (p.R188C and p.W419X) have been identified and associated with congenital pancreatic lipase deficiency in symptomatic children. The aim of this study was to characterize the lipase function and proteotoxicity of these two PNLIP mutants in vitro.

Methods:
We generated a mammalian protein expression construct pcDNA3/PNLIP WT. Next, we made plasmid DNA constructs pcDNA3/PNLIP R188C or W419X by site-directed mutagenesis. We then transfected HEK293T cells to express PNLIP WT, R188C, or W419X. Three days post-transfection, we harvested conditioned media and cells. We assessed secretion of lipase in medium through lipase activity assay and immunoblot against PNLIP. We fractionated the cell lysates into detergent soluble and insoluble fractions to assess PNLIP misfolding and endoplasm reticulum (ER) stress by immunoblot against PNLIP and BiP (an ER stress marker), respectively. 

Results:
The conditioned media from cells expressing PNLIP WT had steady lipase activity whereas the R188C or W419X media lacked detectable lipase activity. Immunoblot revealed a strong PNLIP band in the WT media, but no visible bands in R188C or W419X media. These results suggest the defective secretion of both mutant PNLIP proteins. Moreover, a much higher proportion of PNLIP R188C and W419X was present in the detergent insoluble fraction compared with WT indicating increased misfolding of the PNLIP mutant proteins. Further immunoblot analysis of cell lysates indicated markedly up-regulated BiP in the mutant samples relative to WT controls.

Conclusion:
Our data illustrate that both R188C and W419X mutations in PNLIP result in loss of lipase function due to abolished secretion. Additionally, both mutations may increase the risk to develop chronic pancreatitis through its gain of proteotoxic function. 


Pancreatic Lipase Deficiency: Characterization of Novel PNLIP Mutations

Abstract Title: Dopaminergic contributions to evaluation and reevaluation of neuroeconomic decision making 

Background: Dopamine signaling in the nucleus accumbens core is an important neural substrate for neuroeconomic decision making. Dopamine dynamics reflect reward value, prediction error, and motivation, but have not been studied extensively under conditions of neuroeconomic foraging tasks known to show cognitive consideration of future and past events. Furthermore, decreases in dopamine in settings of internally-driven decision reevaluation have not been reported. 

Methods: Mice were trained on a neuroeconomic foraging task (Restaurant Row) to evaluate offers to earn food rewards. They were given a daily budget of one hour to forage for food rewards of four distinct flavors (restaurants). Upon entering a restaurant, mice first encountered an Offer Zone in which a tone sounded whose pitch signaled the delay the animal would have to wait before reward would be delivered (higher pitched tones signaled longer delays, lower pitched tones signaled shorter delays). After the tone presentation in the Offer Zone, the animal could either accept or reject the offer. To reject the offer, mice would continue to the next corner to receive a new offer for a different flavored pellet. To accept the offer, mice would advance into a Wait Zone, where the countdown to reward began. At any point during the countdown, the animal had the opportunity to quit the trial, and would only earn reward if it waited out the entire delay. 

Using fiber photometry to monitor dopamine dynamics in mice while they performed this neuroeconomic task, we investigated how dopamine encodes evaluation and reevaluation of neuroeconomic decisions. 

Results: Dopamine dynamics in the OZ scaled with the value of the offer in both groups, consistent with descriptions of dopamine’s role in encoding value. Notably, the depth of the dopamine decrease was greatest for worse value offers, reflecting a re-evaluation process. 

Conclusion: Dopamine dynamics during quits reflect a cognitive consideration of the past offer value. This work demonstrates that decreases in dopamine can track a retrospective process wherein mice reevaluate their decision to accept a bad offer. This suggests that dopamine may encode current as well as past value as agents reevaluate and update their decisions.


Next from AMA Research Challenge 2022

Orthopaedic Surgery - Biceps Autograft versus Dermal Allograft for Superior Capsule Reconstruction after Rotator Cuff Tear - Orthopaedic Surgery

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