Magnetosomes are organelle-like structures within magnetotactic bacteria that store iron biominerals in membrane-bound vesicles. In bacteria, formation of these structures is highly regulated by approximately 30 genes, which are conserved throughout different species. To compartmentalize iron in mammalian cells and provide gene-based contrast for magnetic resonance imaging, we introduced key magnetosome proteins. The expression of essential magnetosome genes mamI and mamL as fluorescent fusion proteins in a human melanoma cell line confirmed their co-localization and interaction. Here, we investigate the expression of two more essential magnetosome genes, mamB and mamE, using confocal microscopy to describe fluorescent fusion protein expression patterns and analyze the observed intracellular mobility. Custom software was developed to characterize fluorescent particle trajectories. In mammalian cells, essential magnetosome proteins display different diffusive behaviours. However, all magnetosome proteins travelled at similar velocities when interacting with mammalian mobile elements, suggesting that MamL, MamL + MamI, MamB, and MamE interact with similar molecular motor proteins. These results confirm that localization and interaction of essential magnetosome proteins are feasible within the mammalian intracellular compartment.

To detect cellular activities deep within the body using magnetic resonance (MR) platforms, magnetosomes are the ideal model of genetically-encoded nanoparticles. These organelle-like structures produced by magnetotactic bacteria (MTB) store iron biominerals in membrane-bound vesicles and are highly regulated by approximately 30 genes. To translate this technology into a gene-based iron contrast agent in mammalian cells [1], [2], we are introducing essential membrane-associated magnetosome (mam) genes mamI, mamL, mamB, and mamE into the human melanoma cell line MDA-MB-435 using fluorescent fusion protein vectors. While the expression of enhanced green fluorescent protein (EGFP)-MamI alone resulted in a net-like fluorescence pattern, individual expression of red fluorescent Tomato-MamL, Tomato-MamB, or Tomato-MamE all resulted in a mobile, punctate fluorescence pattern. Coexpression of MamL+I resulted in co-localization of both proteins in a mobile, punctate pattern. Here we report the transient expression of three magnetosome proteins (MamL+I+B or MamL+I+E) in mammalian cells, which results in the co-localization and interaction of all three proteins in a mobile, punctate pattern. These results further support interactions between essential magnetosome proteins in the mammalian intracellular compartment and the co-localization required to form a rudimentary magnetosome-like particle.

To detect cellular activities deep within the body using magnetic resonance platforms, magnetosomes are the ideal model of genetically-encoded nanoparticles. These membrane-bound iron biominerals produced by magnetotactic bacteria are highly regulated by approximately 30 genes; however, the number of magnetosome genes that are essential and/or constitute the root structure upon which biominerals form is largely undefined. To examine the possibility that key magnetosome genes may interact in a foreign environment, we expressed mamI and mamL as fluorescent fusion proteins in mammalian cells. Localization and potential protein-protein interaction(s) were investigated using confocal microscopy and fluorescence correlation spectroscopy (FCS). Enhanced green fluorescent protein (EGFP)-MamI and the red fluorescent Tomato-MamL displayed distinct intracellular localization, with net-like and punctate fluorescence, respectively. Remarkably, co-expression revealed co-localization of both fluorescent fusion proteins in the same punctate pattern. An interaction between MamI and MamL was confirmed by co-immunoprecipitation. In addition, changes in EGFP-MamI distribution were accompanied by acquisition of intracellular mobility which all Tomato-MamL structures displayed. Analysis of extracts from these cells by FCS was consistent with an interaction between fluorescent fusion proteins, including an increase in particle radius. Co-localization and interaction of MamI and MamL demonstrate that select magnetosome proteins may associate in mammalian cells.

Bacteria constitute a significant part of the biomass of the human microbiota, but their interactions are complex and difficult to replicate outside the host. Exploiting the superior resolution of magnetic resonance imaging (MRI) to examine signal parameters of selected human isolates may allow tracking of their dispersion throughout the body. Here we investigate longitudinal and transverse MRI relaxation rates and found significant differences between several bacterial strains. Common commensal strains of lactobacilli display notably high MRI relaxation rates, partially explained by elevated cellular manganese content, while other species contain more iron than manganese. Lactobacillus crispatus show particularly high values, 4-fold greater than any other species; up to 60-fold greater signal than relevant tissue background; and a linear relationship between relaxation rate and fraction of live cells. Different bacterial strains have detectable, repeatable MRI relaxation rates that in the future may enable monitoring of their persistence in the human body for enhanced molecular imaging. In vitro examination of urogenital microbiota by MRI reveals high relaxation rates in lactobacilli and correlates quantity of bacteria with MRI measures that exceed those of the healthy human bladder epithelium.

The magnetosome, a membrane-bound iron biomineral formed within magnetotactic bacteria, is a unique model for a magnetic resonance imaging (MRI) reporter gene contrast agent. We are translating this technology to mammalian cells by expressing essential magnetosome genes mamI, mamL, mamB, and mamE into MDA-MB-435 human melanoma cells. Currently, these genes are individually expressed in the cell although the future goal is to express all four genes together. We examined the influence of these genes on cellular MRI relaxation rates by culturing cells in the presence and absence of iron-supplemented medium and scanning them at 3 Tesla using a gelatin phantom. Total cellular iron was measured by inductively-coupled plasma mass spectrometry and correlated with relaxation rates obtained from phantom experiments. Apart from mamE, magnetosome genes that are individually expressed in mammalian cells grown in iron supplement significantly affected cellular transverse relaxation rates compared to cells grown without iron supplement. Interestingly, mamI, mamL, mamB, and mamE (even though the latter had no effect on relaxation rate) significantly affected cellular iron content. This developing gene-based contrast agent will equip MRI with improvement to imaging sensitivity and the technology to track cellular activities long term.

Many chronic inflammatory conditions are mediated by an increase in the number of monocytes in peripheral circulation, differentiation of monocytes to macrophages, and different macrophage subpopulations during pro- and anti-inflammatory stages of tissue injury. When hepcidin secretion is stimulated during inflammation, the iron export protein ferroportin is targeted for degradation on a limited number of cell types, including monocytes and macrophages. Such changes in monocyte iron metabolism raise the possibility of non-invasively tracking the activity of these immune cells using magnetic resonance imaging (MRI). We hypothesized that hepcidin-mediated changes in monocyte iron regulation influence both cellular iron content and MRI relaxation rates. In response to varying conditions of extracellular iron supplementation, ferroportin protein levels in human THP-1 monocytes decreased two- to eightfold, consistent with paracrine/autocrine regulation of iron export. Following hepcidin treatment, ferroportin protein levels further decreased two- to fourfold. This was accompanied by an approximately twofold increase in total transverse relaxation rate, R2*, compared to non-supplemented cells. A positive correlation between total cellular iron content and R2* improved from moderate to strong in the presence of hepcidin. These findings suggest that hepcidin-mediated changes detected in monocytes using MRI could be valuable for in vivo cell tracking of inflammatory responses.

Purpose/Objective(s) Metastases directed therapy of oligometastatic colorectal cancer (CRC) may confer long-term disease advantages. However, there is a paucity of data to predict optimal patient selection. Our hypothesis is that pretreatment factors can identify patients at higher risk of early progression after SBRT for CRC oligometastases. Materials/Methods An institutional cohort was reviewed to identify patients with extracranial oligometastatic (≤ 5 metastases) colorectal cancer who received SBRT to all metastases. Outcomes of interest were local failure (LF), overall survival (OS) and progression-free survival (PFS). Recursive partitioning analysis (RPA) was performed to identify "early progression", defined as those having a PFS event within 6 months of SBRT, from a training set consisting of 70% of the cohort. The remaining 30% were used in the validation analysis of the model. Results From January 2008 to May 2021, 254 patients were identified with 408 lesions irradiated. Median age was 75 years (IQR: 62-82), median follow-up was 30.5 months (IQR: 17.7-48.8), and median time from diagnosis of cancer to metastatic disease was 12.0 months (IQR: 0.2-26.1). The majority of patients had a single metastasis (n=167, 65.8%). The 12-, 24- and 36-month cumulative incidence of LF was 10.3%, 22.8% and 27.5%, respectively. On multivariable analysis (MVA), liver metastasis (vs. non-liver, HR 1.99, 95%CI: 1.32-3.00, p<0.01) and lower mean PTV dose BED10 (HR: 1.01, 95%CI: 1.01-1.02, p<0.01) predicted for higher LF. Median OS was 51.1 months (95%CI: 46.2-56.3) and 12-, 24- and 36-month OS was 94.0%, 79.5% and 64.9%, respectively. On MVA, higher pre-SBRT CEA (HR: 1.21, 95%CI: 1.01-1.45, p=0.04) and larger PTV volume (HR: 1.61, 95%CI: 1.31-1.97, p<0.01) were significant predictors of worse OS. Median PFS was 11.8 months (95%CI: 9.9-13.7) and 6-, 12- and 24-month PFS was 73.2%, 49.2% and 30.4%, respectively. Of the 254 patients included, 68 (26.8%) had "early progression". The RPA model ranked the following variables in order of importance: presence or history of any liver metastases, pre-SBRT CEA and number of lesions treated at time of SBRT. Four terminal nodes (i.e., groups) were generated, classifying the probability of "early progression" with a training and validation receiver operating characteristic curve (AUC) of 0.72 and 0.71, respectively. The two groups at highest risk of early progression were: 1) history or presence of any liver metastases and with ≥2 lesions treated; and 2) history or presence of any liver metastases with 1 lesion treated at the time of SBRT, and pre-SBRT CEA ≥8 ng/mL. Conclusion History or presence of liver metastases, higher number of lesions, and higher CEA levels can aid in the identification of oligometastatic patients who progress soon after SBRT. Such patients can be considered for alternative treatment strategies.

BACKGROUND: Studies suggest that expose to both air pollution and violence may alter development trajectory, as it may disrupt the HPA-axis which plays an important role in how the human body reacts to environmental stressors affecting sleep. We propose that prenatal air pollution exposure may interact with violence to affect the efficiency of sleep, therefore, modified by exposure to violence. METHODS: We studied 412 children enrolled in Programming Research in Obesity, GRowth, Environment and Social Stressors (PROGRESS), a birth cohort study in Mexico City. We used a spatio-temporal model to estimate individual daily prenatal PM2.5 exposure at each participant's residential address. We assessed the sleep efficiency (defined with time awake divided by time in bed) of all kids at age 4-7 years with assigned accelerometer worn during sleep, and recorded sleep patterns for a week to examine the association between PM2.5 exposure and sleep efficiency. RESULTS: Participants are mostly low SES families (54.6%) with slightly lower proportion of low maternal education (42.1%) and are racial/ethnicity uniformed. Sleep efficiencies are normally distributed and ranging from 63.5 to 91.8. At age 4, children who were exposed to low-to-mid violence are more likely to have their sleep efficiency disrupted by prenatal PM2.5 exposure (ETV at 10%tile, β=-0.26, CI:-1.19,0.68; However, at age 6, we found that PM2.5 reduced sleep efficiency at even lower levels, (ETV at 10%tile, β=-0.26, CI:-1.05,0.54; peak PM effect at ETV at 36%tile, β=-0.71, CI:-1.5,0.09; ETV at 90%tile, β=0.28, CI:-1,1.55; ). CONCLUSION: As the literature expands on sleep and sleep disparities, the sparseness of studies on children's sleep highlights a research void that if addressed could mitigate the adverse impact of child sleep disparities on long term health. KEYWORDS: environmental stressors, violence, sleep health, disparities, exposure

Abstract Background While the available SARS-CoV2 vaccines are up to 94% effective at preventing COVID-19-related death or invasive mechanical ventilation, only 76% of the United States population aged ≥18 years have received a primary series and 49% have received a booster. Vaccine administration has been complicated by changing schedule recommendations, packaging in multi-dose vials, and federal reporting requirements that may have limited the locations offering vaccines. We therefore implemented a pharmacy-based initiative to provide SARS-CoV2 vaccination to patients admitted to an academic health center, in order to encourage vaccination when patients had presented for other care. Methods A pharmacy committee developed a protocol for administering the three authorized SARS-CoV2 vaccines to interested inpatients while minimizing vaccine waste, monitoring for safety events, and providing next dose education. Associated training included multidisciplinary education on requirements related to vaccine Emergency Use Authorization (EUA) status. While developing the protocol, the vaccine committee utilized a temporary procedure to administer vaccines once weekly through review by antimicrobial stewardship pharmacists during August 2021. The protocol went live in September 2021 for inpatient and emergency department sites, with subsequent tracking of the number of doses ordered (stratified by vaccine type and dose number) and number administered. Results From August 3 2021 to March 25 2022, a total of 389 vaccine orders were placed with 302 doses (78%) administered, including 126 Moderna (48 first, 20 second, 15 third, 42 booster, and 1 undesignated), 165 Pfizer/BioNTech (80 first, 24 second, 41 third, 14 booster, and 6 undesignated), and 11 Janssen COVID-19 vaccine doses. Only 18 vaccine orders were placed on patients in the ED, with 14 (78%) of those doses administered. Of the 87 vaccine orders not administered, 6 were placed but not given, and 81 were placed and then discontinued. Conclusion With multidisciplinary collaboration, SARS-CoV2 vaccination can be performed in inpatient and ED settings. However, orders should be monitored for protocol compliance and order discontinuation, as these may increase potential for waste. Disclosures All Authors: No reported disclosures.

Background and purpose: To quantify intra-fraction tumor motion using imageguidance and implanted fiducial markers to determine if a 5 mm planning-target-volume (PTV) margin is sufficient for early stage breast cancer patients receiving neoadjuvant stereotactic ablative radiotherapy (SABR). Materials and methods: A HydroMark (c) (Mammotome) fiducial was implanted at the time of biopsy adjacent to the tumor. Sixty-one patients with 62 tumours were treated prone using a 5 mm PTV margin. Motion was quantified using two methods (separate patient groups): 1) difference in 3D fiducial position pre-and post-treatment cone-beam CTs (CBCTs) in 18 patients receiving 21 Gy/1fraction (fx); 2) acquiring 2D triggered-kVimages to quantify 3D intra-fraction motion using a 2D-to-3D estimation method for 44 tumours receiving 21 Gy/1fx (n = 22) or 30 Gy/3fx (n = 22). For 2), motion was quantified by calculating the magnitude of intra-fraction positional deviation from the pretreatment CBCT. PTV margins were derived using van Herkian analysis. Results: The average +/- standard deviation magnitude of motion across patients was 1.3 +/- 1.15 mm Left/ Right (L/R), 1.0 +/- 0.9 mm Inferiorly/Superiorly (I/S), and 1.8 +/- 1.5 mm Anteriorly/Posteriorly (A/P). 85/105 (81%) treatment fractions had dominant anterior motion. 6/62patients (9.7%) had mean intra-fraction motion during any fraction > 5 mm in any direction, with 4 in the anterior direction. Estimated PTV margins for single and three-fx patients in the L/R, I/S, and A/P directions were 6.0x4.1x5.9 mm and 4.5x2.9x4.3 mm, respectively. Conclusion: Our results suggest that a 5 mm PTV margin is sufficient for the I/S and A/P directions if a lateral kV image is acquired immediately before treatment. For the L/R direction, either further immobilization or a larger margin is required. (c) 2021 Elsevier B.V. All rights reserved. Radiotherapy and Oncology 158 (2021) 276-284

OBJECTIVE:Hybrid PET/MRI may improve detection of seizure-onset zone (SOZ) in drug-resistant epilepsy (DRE), however, concerns over PET bias from MRI-based attenuation correction (MRAC) have limited clinical adoption of PET/MRI. This study evaluated the diagnostic equivalency and potential clinical value of PET/MRI against PET/CT in DRE.MATERIALS AND METHODS:MRI, FDG-PET and CT images (n = 18) were acquired using a hybrid PET/MRI and a CT scanner. To assess diagnostic equivalency, PET was reconstructed using MRAC (RESOLUTE) and CT-based attenuation correction (CTAC) to generate PET/MRI and PET/CT images, respectively. PET/MRI and PET/CT images were compared qualitatively through visual assessment and quantitatively through regional standardized uptake value (SUV) and z-score assessment. Diagnostic accuracy and sensitivity of PET/MRI and PET/CT for SOZ detection were calculated through comparison to reference standards (clinical hypothesis and histopathology, respectively).RESULTS:Inter-reader agreement in visual assessment of PET/MRI and PET/CT images was 78 % and 81 %, respectively. PET/MRI and PET/CT were strongly correlated in mean SUV (r = 0.99, p < 0.001) and z-scores (r = 0.92, p < 0.001) across all brain regions. MRAC SUV bias was <5% in most brain regions except the inferior temporal gyrus, temporal pole, and cerebellum. Diagnostic accuracy and sensitivity were similar between PET/MRI and PET/CT (87 % vs. 85 % and 83 % vs. 83 %, respectively).CONCLUSION:We demonstrate here that PET/MRI with optimal MRAC can yield similar diagnostic performance as PET/CT. Nevertheless, further exploration of the potential added value of PET/MRI is necessary before clinical adoption of PET/MRI for epilepsy imaging.

Magnetic resonance imaging can be used to track cellular activities in the body using iron-based contrast agents. However, multiple intrinsic cellular iron handling mechanisms may also influence the detection of magnetic resonance (MR) contrast: a need to differentiate among those mechanisms exists. In hepcidin-mediated inflammation, for example, downregulation of iron export in monocytes and macrophages involves post-translational degradation of ferroportin. We examined the influence of hepcidin endocrine activity on iron regulation and MR transverse relaxation rates in multi-potent P19 cells, which display high iron import and export activities, similar to alternatively-activated macrophages. Iron import and export were examined in cultured P19 cells in the presence and absence of iron-supplemented medium, respectively. Western blots indicated the levels of transferrin receptor, ferroportin and ubiquitin in the presence and absence of extracellular hepcidin. Total cellular iron was measured by inductively-coupled plasma mass spectrometry and correlated to transverse relaxation rates at 3 Tesla using a gelatin phantom. Under varying conditions of iron supplementation, the level of ferroportin in P19 cells responds to hepcidin regulation, consistent with degradation through a ubiquitin-mediated pathway. This response of P19 cells to hepcidin is similar to that of classically-activated macrophages. The correlation between total cellular iron content and MR transverse relaxation rates was different in hepcidin-treated and untreated P19 cells: slope, Pearson correlation coefficient and relaxation rate were all affected. These findings may provide a tool to non-invasively distinguish changes in endogenous iron contrast arising from hepcidin-ferroportin interactions, with potential utility in monitoring of different macrophage phenotypes involved in pro- and anti-inflammatory signaling. In addition, this work demonstrates that transverse relaxivity is not only influenced by the amount of cellular iron but also by its metabolism.

BACKGROUND:Simultaneous cardiovascular imaging with positron emission tomography (PET) and magnetic resonance imaging (MRI) requires tools such as radio frequency (RF) phased arrays to achieve high temporal and spatial resolution in the MRI, as well as accurate quantification of PET. Today, high-density phased arrays (> 16 channels) used for cardiovascular PET/MRI are not designed to achieve low PET attenuation, and correcting the PET attenuation they cause requires off-line reconstruction, extra time and resources.PURPOSE:Motivated by previous work assessing the MRI performance of a novel prospectively designed 32-channel phased array, this study assessed the PET image quality with this array in place. Guided by NEMA standards, PET performance was measured using global PET counts, regional background variation (BV), contrast recovery (CR) and contrast-to-noise ratio (CNR) for both the novel array and standard arrays (mMR 12-channel and MRI 32-channel). Nonattenuation-corrected (NAC) data from all arrays (and each part of the array) were processed and compared to no-array, and relative percentage difference (RPD) of the global means was estimated and reported for each part of the arrays. Attenuation correction (AC) of PET images (water in the phantom) using two approaches, MR-based AC map (MRAC) and dual-energy CT-based map (DCTAC), was performed, and RPD compared for each part of the arrays. Percent mean attenuation within regions of interests of the phantom images from each array were compared using a two-way analysis of variance (ANOVA).RESULTS:The NAC data of the anterior part of the novel array recorded the least PET attenuation (≤ 2%); while the full novel array (anterior and posterior together) AC data, produced by MRAC and DCTAC approaches, recorded attenuation of 1.5 ± 2.9% and 0.0 ± 2.5%, respectively. The novel array PET count loss was significantly lower (p = 0.001) than those caused by the standard arrays.CONCLUSIONS:Results of this novel 32-channel cardiac array PET performance evaluation, together with its previously reported MRI performance assessment, suggest the novel array to be a strong alternative to the standard arrays currently used for cardiovascular hybrid PET/MRI imaging. It enables accurate PET quantification and high-temporal and spatial resolution for MR imaging.

BackgroundCardiovascular imaging using hybrid positron emission tomography (PET) and magnetic resonance imaging (MRI) requires a radio frequency phased array resonator capable of high acceleration factors in order to achieve the shortest breath-holds while maintaining optimal MRI signal-to-noise ratio (SNR) and minimum PET photon attenuation. To our knowledge, the only two arrays used today for hybrid PET/MRI cardiovascular imaging are either incapable of achieving high acceleration or affect the PET photon count greatly.PurposeThis study is focused on the evaluation of the MRI performance of a novel third-party prototype 32-channel phased array designed for simultaneous PET/MRI cardiovascular imaging. The study compares the quality parameters of MRI parallel imaging, such as g-factor, noise correlation coefficients, and SNR, to the conventional arrays (mMR 12-channel and MRI-only 32-channel) currently used with hybrid PET/MRI systems. The quality parameters of parallel imaging were estimated for multiple acceleration factors on a phantom and three healthy volunteers. Using a Germanium-68 (Ge-68) phantom, preliminary measurements of PET photon attenuation caused by the novel array were briefly compared to the photon counts produced from no-array measurements.ResultsThe global mean of the g-factor and SNRg produced by the novel 32-channel PET/MRI array were better than those produced by the MRI-only 32-channel array by 5% or more. The novel array has resulted in MRI SNR improvements of >30% at all acceleration factors, in comparison to the mMR12-channel array. Preliminary evaluation of PET transparency showed less than 5% photon attenuation caused by both anterior and posterior parts of the novel array.ConclusionsThe MRI performance of the novel PET/MRI 32-channel array qualifies it to be a viable alternative to the conventional arrays for cardiovascular hybrid PET/MRI. A detailed evaluation of the novel array's PET performance remains to be conducted, but cursory assessment promises significantly reduced attenuation.

Purpose or ObjectiveSquamous cell cancer of the anus is associated with multiple risk factors, including infection with human papillomavirus [HPV] and human immunodeficiency virus, immunosuppression, multiple sex partners, receptive anal sex and tobacco smoking.The aim of our study was to identify prognostic factors associated with poor outcome after radiotherapy for anal cancer. Material and MethodsWe analysed retrospectively the medical records of 171 patients treated by (chemo)-radiotherapy for a nonmetastatic anal cancer in our institution from 2000 to 2015.Patients and tumor characteristics, treatments (chemotherapy (CT), radiotherapy (RT), and surgery) and outcomes were analyzed.Colostomy-free, disease-free and overall survivals at 5 years were studied.Univariate and multivariate analyses were performed by logistic regression in order to determine factors associated with poor progression free survival (PFS). ResultsPatients characteristics were as follow: median age: 62 years (range 36-89); gender: 45 males (26%) and 126 females (74%); HIV serology: positive 21 patients (12%), negative or unknown 150 patients (88%); tobacco smoking: 86 Pts (50%) among whom 28 Pts and 58 Pts were current and former smokers respectively.Tumors were classified as locally limited (T0-1-2, N0, M0) for 86 pts (50%) and locally advanced (T3-4 or N+, M0) for 85 pts (50%).Median total dose was 64.4 Gy (range 54-76.6),146 patients were treated by concurrent chemoradiotherapy.Factors associated with poor PFS in univariate analysis were: tumor size >4cm, lymph node involvement; tobacco smoking, no initial surgical excision and anal warts at diagnosis.In multivariate analysis, only tobacco smoking status was significantly associated with poor PFS (HR=2.85 [1.25-6.50],p=0.013).5-years-PFS for non-smokers, former smokers and current smokers was 88.1%, 76,7% and 73.8% respectively (p=0.038).Tobacco smoking was also associated with poor overall survival (p=0.03) and colostomy free survival (p=0.02). ConclusionTobacco smoking status is associated with poor overall survival, PFS and colostomy free survival in patients treated for anal cancer by (chemo)-radiotherapy.

Magnetic resonance imaging (MRI) is a non-invasive imaging modality used in longitudinal cell tracking. Previous studies suggest that MagA, a putative iron transport protein from magnetotactic bacteria, is a useful gene-based magnetic resonance contrast agent. Hemagglutinin-tagged MagA was stably expressed in undifferentiated embryonic mouse teratocarcinoma, multipotent P19 cells to provide a suitable model for tracking these cells during differentiation. Western blot and immunocytochemistry confirmed the expression and membrane localization of MagA in P19 cells. Surprisingly, elemental iron analysis using inductively-coupled plasma mass spectrometry revealed significant iron uptake in both parental and MagA-expressing P19 cells, cultured in the presence of iron-supplemented medium. Withdrawal of this extracellular iron supplement revealed unexpected iron export activity in P19 cells, which MagA expression attenuated. The influence of iron supplementation on parental and MagA-expressing cells was not reflected by longitudinal relaxation rates. Measurement of transverse relaxation rates (R2* and R2) reflected changes in total cellular iron content but did not clearly distinguish MagA-expressing cells from the parental cell type, despite significant differences in the uptake and retention of total cellular iron. Unlike other cell types, the reversible component R2' (R2* ‒ R2) provided only a moderately strong correlation to amount of cellular iron, normalized to amount of protein. This is the first report to characterize MagA expression in a previously unrecognized iron exporting cell type. The interplay between contrast gene expression and systemic iron metabolism substantiates the potential for diverting cellular iron toward the formation of a novel iron compartment, however rudimentary when using a single magnetotactic bacterial gene expression system like magA. Since relatively few mammalian cells export iron, the P19 cell line provides a tractable model of ferroportin activity, suitable for magnetic resonance analysis of key iron-handling activities and their influence on gene-based MRI contrast.

Magnetic resonance imaging (MRI) T2 and T1ρ relaxation are increasingly being proposed as imaging biomarkers potentially capable of detecting biochemical changes in articular cartilage before structural changes are evident. We aimed to: 1) summarize MRI methods of published studies investigating T2 and T1ρ relaxation time in participants at risk for but without radiographic knee OA; and 2) compare T2 and T1ρ relaxation between participants at-risk for knee OA and healthy controls. We conducted a systematic review of studies reporting T2 and T1ρ relaxation data that included both participants at risk for knee OA and healthy controls. Participant characteristics, MRI methodology, and T1ρ and T2 relaxation data were extracted. Standardized mean differences (SMDs) were calculated within each study. Pooled effect sizes were then calculated for six commonly segmented knee compartments. 55 articles met eligibility criteria. There was considerable variability between scanners, coils, software, scanning protocols, pulse sequences, and post-processing. Moderate risk of bias due to lack of blinding was common. Pooled effect sizes indicated participants at risk for knee OA had lengthened T2 relaxation time in all compartments (SMDs from 0.33 to 0.74; p < 0.01) and lengthened T1ρ relaxation time in the femoral compartments (SMD from 0.35 to 0.40; p < 0.001). T2 and T1ρ relaxation distinguish participants at risk for knee OA from healthy controls. Greater standardization of MRI methods is both warranted and required for progress towards biomarker validation.