Citations

Abstract Background Magnetic Resonance‐guided Radiation Therapy (MRgRT) systems are increasingly used in clinical practice, necessitating a dedicated dosimetry protocol to address the challenges posed by the presence of strong magnetic fields. Purpose AAPM TG351 introduces a reference dosimetry protocol for external beam MRgRT systems, aligning with AAPM TG51 reports and incorporating elements from the IAEA TRS398 code of practice. Methods The protocol offers practical guidance on beam quality and dosimetry setup in the presence of strong magnetic fields. It reviews relevant literature to identify reference‐class chambers suitable for external beam MRgRT systems and determines their beam quality conversion and other relevant correction factors through a detailed analysis of available data and associated uncertainties. Results AAPM TG351 offers a comprehensive dosimetry protocol for external beam MRgRT systems, addressing the unique challenges posed by the presence of magnetic fields. It includes detailed guidance for measurement setups, a list of reference‐class chambers appropriate for reference dosimetry in MRgRT systems, and updated beam quality conversion and correction factors. Additionally, the protocol presents an in‐depth analysis of the uncertainty budget, identifying key contributors and providing strategies to minimize uncertainties, thereby enhancing clinical accuracy and reliability. Conclusions This protocol provides a practical, evidence‐based reference for medical physicists conducting reference dosimetry in external beam MRgRT systems.

Background Atherosclerosis is highly prevalent in people with chronic kidney disease (CKD), including those receiving peritoneal dialysis (PD). Although it is lifesaving, PD induces profound systemic inflammation, which may aggravate atherosclerosis. Therefore, the hypothesis is that this PD‐induced inflammation aggravates atherosclerosis via immune cell activation. Methods and Results ApoE −/− mice were subjected to a 5/6 nephrectomy to induce CKD. Three weeks later, mice were fed a high‐cholesterol diet. Half of the nephrectomized mice then received daily peritoneal infusions of 3.86% Physioneal for 67 further days (CKD+PD) until the end of the experiment, and were compared with mice without CKD. Sham operated and PD‐only mice were additional controls. CKD+PD mice displayed more severe atherosclerotic disease than control mice. Plaque area increased, and plaques were more advanced with a vulnerable phenotype typified by decreased collagen content and decreased fibrous cap thickness. Increased CD3 + T‐cell numbers were present in plaques and perivascular adipose tissue of CKD and CKD+PD mice. Plaques of CKD+PD mice contained more iNOS + immune cells. Spleens of CKD+PD mice showed more CD4 + central memory, terminally differentiated type 1 T‐helper (Th1), Th17, and CX3C motif chemokine receptor 1 + (CX3CR1) CD4 + T‐cells with less regulatory and effector T‐cells. Conclusions PD‐fluid exposure in uremic mice potentiates systemic and vascular T‐cell‐driven inflammation and aggravates atherosclerosis. PD polarized CD4 + T‐cells toward an inflammatory Th1/Th17 phenotype, and increased CX3CR1 + CD4 + T‐cells, which are associated with vascular homing in CKD‐associated atherosclerosis. Targeting CD4 + T‐cell activation and CX3CR1 + polarization has the potential to attenuate atherosclerosis in PD patients.

Abstract Background and Aims Inflammation is an established contributor to accelerated atherosclerosis, which is highly prevalent in people with chronic kidney disease (CKD) and even more so in those treated with peritoneal dialysis (PD). We therefore hypothesised that PD-induced systemic inflammation is essential in the development of atherosclerosis. To study this we developed a novel mouse model of CKD and PD accelerated atherosclerosis. Method We performed a 5/6ths nephrectomy in ApoE deficient “black 6” mice, fed these mice a high-cholesterol diet (HCD), and intraperitoneally administered 3.86% Physioneal daily for 67 days. There were three groups of mice: control (HCD-only), CKD+HCD, and CKD+HCD+PD, with relevant shams. Tissues were harvested twelve weeks after the nephrectomy. Assessments of residual kidney function, atherosclerotic plaque pathology and immunology, and systemic immune responses were performed. Results Atherosclerotic plaque size in the aortic arch was larger in the PD group compared to the control, increasing from 83,779 μm2 ±18,430 to 109,973 μm2 ±25,602 (p = 0.0349), whilst plaque size was unchanged in the CKD group. In contrast, both the CKD and PD groups displayed altered plaque stability. There was less collagen in the plaque vs control, decreasing from 43.54% ±10.65 to 29.71% ±9.43 and 29.73% ±10.18 respectively. Additionally, fibrous cap thickness decreased in both groups vs control. The plaques from only the PD group showed infiltration by T-cells compared to control, with no changes in macrophage content in either the CKD or PD group. In the spleen in the CKD and PD groups, naïve CD4 cells increased and effector CD4 cells decreased compared to control, with the latter change also occurring in the circulation. Central memory CD4 cells, terminally differentiated Th1 cells, Th17 cells, and ‘vascular homing’ cells all increased in the PD group compared to control mice. These homing cells also increased in circulation. The PD group showed decreases in the spleen of regulatory T-cells, effector Th1 cells, and effector CD8 cells. Notably, all of these changes were absent from the mesenteric lymph node. There was a large drop in monocytes in the spleen and a loss of immature and mature dendritic cells in the PD group. Conclusion Combining CKD, a high-cholesterol diet, and exposure to PD fluids in ApoE−/-mice successfully generated a new model for cardiovascular disease in human PD patients. This new model is in a widespread and well-understood mouse line representative of human atherosclerosis. Here we demonstrate the pronounced effects of CKD and PD on the innate and adaptive immune response which increases atherosclerotic burden and leads to larger more vulnerable plaques

Abstract Aims Hyperlipidemia and T cell driven inflammation are important drivers of atherosclerosis, the main underlying cause of cardiovascular disease. Here, we detailed the effects of hyperlipidemia on T cells. Methods and results In vitro, exposure of human and murine CD4+ T cells to very low-density lipoprotein (VLDL), but not to low-density lipoprotein (LDL) resulted in upregulation of Th1 associated pathways. VLDL was taken up via a CD36-dependent pathway and resulted in membrane stiffening and a reduction in lipid rafts. To further detail this response in vivo, T cells of mice lacking the LDL receptor (LDLr), which develop a strong increase in VLDL cholesterol and triglyceride levels upon high cholesterol feeding were investigated. CD4+ T cells of hyperlipidemic Ldlr-/- mice exhibited an increased expression of the C-X-C-chemokine receptor 3 (CXCR3) and produced more interferon-γ (IFN-γ). Gene set enrichment analysis identified IFN-γ-mediated signaling as the most upregulated pathway in hyperlipidemic T cells. However, the classical Th1 associated transcription factor profile with strong upregulation of Tbet and Il12rb2 was not observed. Hyperlipidemia did not affect levels of the CD4+ T cell's metabolites involved in glycolysis or other canonical metabolic pathways but enhanced amino acids levels. However, CD4+ T cells of hyperlipidemic mice showed increased cholesterol accumulation and an increased arachidonic acid (AA) to docosahexaenoic acid (DHA) ratio, which was associated with inflammatory T cell activation. Conclusions Hyperlipidemia, and especially its VLDL component induces an atypical Th1 response in CD4+ T cells. Underlying mechanisms include CD36 mediated uptake of VLDL, and an altered AA/DHA ratio.

AbstractArboviruses target bone forming osteoblasts and perturb bone remodeling via paracrine factors. We previously reported that Zika virus (ZIKV) infection of early‐stage human mesenchymal stromal cells (MSCs) inhibited the osteogenic lineage commitment of MSCs. To understand the physiological interplay between bone development and ZIKV pathogenesis, we employed a primary in vitro model to examine the biological responses of MSCs to ZIKV infection at different stages of osteogenesis. Precommitted MSCs were infected at the late stage of osteogenic stimulation (Day 7) with ZIKV (multiplicity of infection of 5). We observe that MSCs infected at the late stage of differentiation are highly susceptible to ZIKV infection similar to previous observations with early stage infected MSCs (Day 0). However, in contrast to ZIKV infection at the early stage of differentiation, infection at a later stage significantly elevates the key osteogenic markers and calcium content. Comparative RNA sequencing (RNA‐seq) of early and late stage infected MSCs reveals that ZIKV infection alters the mRNA transcriptome during osteogenic induction of MSCs (1251 genes). ZIKV infection provokes a robust antiviral response at both stages of osteogenic differentiation as reflected by the upregulation of interferon responsive genes (n > 140). ZIKV infection enhances the expression of immune‐related genes in early stage MSCs while increasing cell cycle genes in late stage MSCs. Remarkably, ZIKA infection in early stage MSCs also activates lipid metabolism‐related pathways. In conclusion, ZIKV infection has differentiation stage‐dependent effects on MSCs and this mechanistic understanding may permit the development of new therapeutic or preventative measures for bone‐related effects of ZIKV infection.

Abstract Aims CD40 and its ligand, CD40L, play a critical role in driving atherosclerotic plaque development. Disrupted CD40-signalling reduces experimental atherosclerosis and induces a favourable stable plaque phenotype. We recently showed that small molecule-based inhibition of CD40-tumour necrosis factor receptor associated factor-6 interactions attenuates atherosclerosis in hyperlipidaemic mice via macrophage-driven mechanisms. The present study aims to detail the function of myeloid CD40 in atherosclerosis using myeloid-specific CD40-deficient mice. Method and Results Cd40flox/flox and LysM-cre Cd40flox/flox mice on an Apoe−/− background were generated (CD40wt and CD40mac−/−, respectively). Atherosclerotic lesion size, as well as plaque macrophage content, was reduced in CD40mac−/− compared to CD40wt mice, and their plaques displayed a reduction in necrotic core size. Transcriptomics analysis of the CD40mac−/− atherosclerotic aorta revealed downregulated pathways of immune pathways and inflammatory responses. Loss of CD40 in macrophages changed the representation of aortic macrophage subsets. Mass cytometry analysis revealed a higher content of a subset of alternative or resident-like CD206+CD209b− macrophages in the atherosclerotic aorta of CD40mac−/− compared to CD40wt mice. RNA-sequencing of bone marrow-derived macrophages of CD40mac−/− mice demonstrated upregulation of genes associated with alternatively activated macrophages (including Folr2, Thbs1, Sdc1, and Tns1). Conclusions We here show that absence of CD40 signalling in myeloid cells reduces atherosclerosis and limits systemic inflammation by preventing a shift in macrophage polarization towards pro-inflammatory states. Our study confirms the merit of macrophage-targeted inhibition of CD40 as a valuable therapeutic strategy to combat atherosclerosis.

AbstractSkeletal muscle‐related symptoms are common in both acute coronavirus disease (Covid)‐19 and post‐acute sequelae of Covid‐19 (PASC). In this narrative review, we discuss cellular and molecular pathways that are affected and consider these in regard to skeletal muscle involvement in other conditions, such as acute respiratory distress syndrome, critical illness myopathy, and post‐viral fatigue syndrome. Patients with severe Covid‐19 and PASC suffer from skeletal muscle weakness and exercise intolerance. Histological sections present muscle fibre atrophy, metabolic alterations, and immune cell infiltration. Contributing factors to weakness and fatigue in patients with severe Covid‐19 include systemic inflammation, disuse, hypoxaemia, and malnutrition. These factors also contribute to post‐intensive care unit (ICU) syndrome and ICU‐acquired weakness and likely explain a substantial part of Covid‐19‐acquired weakness. The skeletal muscle weakness and exercise intolerance associated with PASC are more obscure. Direct severe acute respiratory syndrome coronavirus (SARS‐CoV)‐2 viral infiltration into skeletal muscle or an aberrant immune system likely contribute. Similarities between skeletal muscle alterations in PASC and chronic fatigue syndrome deserve further study. Both SARS‐CoV‐2‐specific factors and generic consequences of acute disease likely underlie the observed skeletal muscle alterations in both acute Covid‐19 and PASC.

Abstract Osteolineage cell‐derived extracellular vesicles (EVs) play a regulatory role in hematopoiesis and have been shown to promote the ex vivo expansion of human hematopoietic stem and progenitor cells (HSPCs). Here, we demonstrate that EVs from different human osteolineage sources do not have the same HSPC expansion promoting potential. Comparison of stimulatory and non‐stimulatory osteolineage EVs by next‐generation sequencing and mass spectrometry analyses revealed distinct microRNA and protein signatures identifying EV‐derived candidate regulators of ex vivo HSPC expansion. Accordingly, the treatment of umbilical cord blood‐derived CD34 + HSPCs with stimulatory EVs‐altered HSPC transcriptome, including genes with known roles in cell proliferation. An integrative bioinformatics approach, which connects the HSPC gene expression data with the candidate cargo in stimulatory EVs, delineated the potentially targeted biological functions and pathways during hematopoietic cell expansion and development. In conclusion, our study gives novel insights into the complex biological role of EVs in osteolineage cell‐HSPC crosstalk and promotes the utility of EVs and their cargo as therapeutic agents in regenerative medicine.