Lymphatic System Flows

Comparison of peracetic acid and bacteriophage application by vascular rinsing on Salmonella reduction in lymph nodes of goat carcasses

The ability of carcass vascular rinsing supplemented with bacteriophage (BP) and peracetic acid (PAA) to reduce Salmonella in lymph nodes (LNs) from experimentally infected goats was determined. Cull dairy goats (n = 60) were randomly assigned to a control (CN, nonrinsed) and two vascular rinse treatments: BP and PAA. Goats were inoculated intradermally with Salmonella Enteritidis and slaughtered after a 7-day incubation. Vascular rinsing was performed postexsanguination via a catheter in the heart. Carcasses were skinned, eviscerated, sprayed with 5% lactic acid, and chilled (2°C) overnight. The superficial cervical, popliteal, medial iliac, and subiliac LNs were collected aseptically for Salmonella enumeration and phage titer determination. The longissimus dorsi (LD) and semimembranosus muscles were also excised, and stored for 1, 4, and 7 days for meat surface color measurements. PAA-treated carcasses showed lower (p < 0.05) temperatures and pH values within 8 h postmortem compared to CN and BP. The average counts of Salmonella in the LNs associated with PAA (3.4 ± 1.3 log CFU/g) were significantly lower compared to CN (3.8 ± 1.1 log CFU/g), with the lowest load observed in medial iliac LNs (2.7 ± 1.5 log CFU/g). Substantial phage titers were detected in LNs from BP-treated carcasses (7.0 ± 0.91 log PFU/g), and no differences were observed in Salmonella counts in BP compared to CN. The meat samples obtained from PAA-treated carcasses exhibited lower redness (a* values) and deoxymyoglobin in the LD (p < 0.05) but showed no differences in lightness or oxymyoglobin compared to BP and CN. Vascular rinsing has the potential to suppress Salmonella in the LNs with other antimicrobials and chemicals with different combinations and concentrations. PRACTICAL APPLICATION: This study investigates a method to control Salmonella in goat meat by rinsing carcasses with peracetic acid (PAA) or bacteriophages through the bloodstream after slaughter. The findings suggest that PAA can mitigate Salmonella levels in lymph nodes, potentially improving meat safety. While bacteriophage treatment did not significantly affect the bacterial count to observe differences with the control group, vascular rinsing could still be promising with different antimicrobial combinations. This research would help meat processors enhance food safety measures, reducing the risk of Salmonella contamination in meat products.

A MPET2-mPBPK model for subcutaneous injection of biotherapeutics with different molecular weights: From local scale to whole-body scale

BACKGROUND AND OBJECTIVE

Subcutaneous injection of biotherapeutics has attracted considerable attention in the pharmaceutical industry. However, there is limited understanding of the mechanisms underlying the absorption of drugs with different molecular weights and the delivery of drugs from the injection site to the targeted tissue.

METHODS

We propose the MPET2-mPBPK model to address this issue. This multiscale model couples the MPET2 model, which describes subcutaneous injection at the local tissue scale from a biomechanical view, with a post-injection absorption model at injection site and a minimal physiologically-based pharmacokinetic (mPBPK) model at whole-body scale. Utilizing the principles of tissue biomechanics and fluid dynamics, the local MPET2 model provides solutions that account for tissue deformation and drug absorption in local blood vessels and initial lymphatic vessels during injection. Additionally, we introduce a model accounting for the molecular weight effect on the absorption by blood vessels, and a nonlinear model accounting for the absorption in lymphatic vessels. The post-injection model predicts drug absorption in local blood vessels and initial lymphatic vessels, which are integrated into the whole-body mPBPK model to describe the pharmacokinetic behaviors of the absorbed drug in the circulatory and lymphatic system.

RESULTS

We establish a numerical model which links the biomechanical process of subcutaneous injection at local tissue scale and the pharmacokinetic behaviors of injected biotherapeutics at whole-body scale. With the help of the model, we propose an explicit relationship between the reflection coefficient and the molecular weight and predict the bioavalibility of biotherapeutics with varying molecular weights via subcutaneous injection.

CONCLUSION

The considered drug absorption mechanisms enable us to study the differences in local drug absorption and whole-body drug distribution with varying molecular weights. This model enhances the understanding of drug absorption mechanisms and transport routes in the circulatory system for drugs of different molecular weights, and holds the potential to facilitate the application of computational modeling to drug formulation.

PSMA Accumulation in Lower Extremity Lymphedema and Hydrocele

ABSTRACT

The development of radiolabeled small-molecule prostate-specific membrane antigen (PSMA) inhibitors has advanced molecular imaging in prostate cancer. The use of 177 Lu-PSMA is especially beneficial because its therapeutic β-emission combined with γ-radiation enables precise treatment and comprehensive imaging in patients with prostate cancer. We present a case of a prostate cancer patient who developed lower extremity lymphedema and hydrocele secondary to prior radiotherapy. Posttherapy whole-body imaging following 177 Lu-PSMA treatment revealed dermal backflow with a notable accumulation of soft tissue in the lower extremities and hydrocele.

Differential impact of lymphatic outflow pathways on cerebrospinal fluid homeostasis

Dysfunctional lymphatic drainage from the central nervous system (CNS) has been linked to neuroinflammatory and neurodegenerative disorders, but our understanding of the lymphatic contribution to CNS fluid autoregulation remains limited. Here, we studied forces that drive the outflow of the cerebrospinal fluid (CSF) into the deep and superficial cervical lymph nodes (dcLN and scLN) and tested how the blockade of lymphatic networks affects CNS fluid homeostasis. Outflow to the dcLN occurred spontaneously in the absence of lymphatic pumping and was coupled to intracranial pressure (ICP), whereas scLN drainage was driven by pumping. Impaired dcLN drainage led to elevated CSF outflow resistance and delayed CSF-to-blood efflux despite the recruitment of the nasal-to-scLN pathway. Fluid regulation was better compensated after scLN obstruction. The dcLN pathway exhibited steady, consistent drainage across conditions, while the nasal-to-scLN pathway was dynamically activated to mitigate perturbances. These findings highlight the complex physiology of CSF homeostasis and lay the groundwork for future studies aimed at assessing and modulating CNS lymphatic function.

Modelling pacemaker oscillations in lymphatic muscle cells: lengthened action potentials by two distinct system effects

Lymphatic system failures contribute to cardiovascular and various other diseases. A critical function of the lymphatic vascular system is the active pumping of fluid from the interstitium back into the blood circulation by periodic contractions of lymphatic muscle cells (LMCs) in the vessel walls. As in cardiac pacemaking, these periodic contractions can be interpreted as occurring due to linked pacemaker oscillations in the LMC membrane potential (M-clock) and calcium concentration (C-clock). We previously reported a minimal model of synchronized dual-clock-driven oscillations. While this qualitatively replicated the period of oscillations under different conditions, it did not replicate the action potential shape as it varied under those conditions, particularly as regards the extent or lack of a systolic plateau. Here, we modify the model to replicate the plateau behaviour. Using phase-plane analysis we show two qualitatively different dynamical mechanisms that could account for plateau formation, one largely M-clock-driven, the other largely C-clock-driven. The second case occurs with the introduction of a ryanodine receptor; in both cases, we find improved predictions for calcium levels. With enhanced fidelity to the experimental data, the improved model has the potential to help determine opportunities for pharmacological treatment of lymphatic system pumping defects.

Lumped parameter simulations of cervical lymphatic vessels: dynamics of murine cerebrospinal fluid efflux from the skull

BACKGROUND

Growing evidence suggests that for rodents, a substantial fraction of cerebrospinal fluid (CSF) drains by crossing the cribriform plate into the nasopharyngeal lymphatics, eventually reaching the cervical lymphatic vessels (CLVs). Disruption of this drainage pathway is associated with various neurological disorders.

METHODS

We employ a lumped parameter method to numerically model CSF drainage across the cribriform plate to CLVs. Our model uses intracranial pressure as an inlet pressure and central venous blood pressure as an outlet pressure. The model incorporates initial lymphatic vessels (modeling those in the nasal region) that absorb the CSF and collecting lymphatic vessels (modeling CLVs) to transport the CSF against an adverse pressure gradient. To determine unknown parameters such as wall stiffness and valve properties, we utilize a Monte Carlo approach and validate our simulation against recent in vivo experimental measurements.

RESULTS

Our parameter analysis reveals the physical characteristics of CLVs. Our results suggest that the stiffness of the vessel wall and the closing state of the valve are crucial for maintaining the vessel size and volume flow rate observed in vivo. We find that a decreased contraction amplitude and frequency leads to a reduction in volume flow rate, and we test the effects of varying the different pressures acting on the CLVs. Finally, we provide evidence that branching of initial lymphatic vessels may deviate from Murray's law to reduce sensitivity to elevated intracranial pressure.

CONCLUSIONS

This is the first numerical study of CSF drainage through CLVs. Our comprehensive parameter analysis offers guidance for future numerical modeling of CLVs. This study also provides a foundation for understanding physiology of CSF drainage, helping guide future experimental studies aimed at identifying causal mechanisms of reduction in CLV transport and potential therapeutic approaches to enhance flow.

Periodic Flows in Microfluidics

Microfluidics, the science and technology of manipulating fluids in microscale channels, offers numerous advantages, such as low energy consumption, compact device size, precise control, fast reaction, and enhanced portability. These benefits have led to applications in biomedical assays, disease diagnostics, drug discovery, neuroscience, and so on. Fluid flow within microfluidic channels is typically in the laminar flow region, which is characterized by low Reynolds numbers but brings the challenge of efficient mixing of fluids. Periodic flows are time-dependent fluid flows, featuring repetitive patterns that can significantly improve fluid mixing and extend the effective length of microchannels for submicron and nanoparticle manipulation. Besides, periodic flow is crucial in organ-on-a-chip (OoC) for accurately modeling physiological processes, advancing disease understanding, drug development, and personalized medicine. Various techniques for generating periodic flows have been reported, including syringe pumps, peristalsis, and actuation based on electric, magnetic, acoustic, mechanical, pneumatic, and fluidic forces, yet comprehensive reviews on this topic remain limited. This paper aims to provide a comprehensive review of periodic flows in microfluidics, from fundamental mechanisms to generation techniques and applications. The challenges and future perspectives are also discussed to exploit the potential of periodic flows in microfluidics.

Lymphedema: Current Strategies for Diagnostics and Management

ABSTRACT

Lymphedema (LE) is characterized by the accumulation of lymph in the extremities, impairing functionality and quality of life. Despite its prevalence, accurate diagnoses and management remains complex because of inconsistencies in diagnostic criteria and limited epidemiological studies. This review aims to address this gap by providing a comprehensive overview of LE classifications, diagnostic approaches, and current management strategies. By synthesizing existing knowledge, this study seeks to contribute to a deeper understanding of LE for improvement of clinical consistency and education.

The paravertebral lymphatic system is involved in the resorption of the herniated nucleus pulposus and the regression of inflammation associated with disc herniation

OBJECTIVE

To investigate the role of the paravertebral lymphatic system in the nucleus pulposus herniation (NPH) resorption and the inflammation regression.

DESIGN

Clinical specimens (n = 10) from patients with lumbar disc herniation (LDH) were collected, C57BL/6 (n = 84) and conditional Vegfr3 knockout mice (n = 14) were used. Immunofluorescence staining detected lymphatic vessels (LVs) and NP cells. Near-infrared imaging assessed lymphatic drainage function, and Alcian Blue/Orange determined inflammation.

RESULTS

Lymphangiogenesis was observed in the herniated NP of patients with LDH, and the proportion of capillary LVs was higher than that of collecting LVs (mean 68.2% [95% confidence interval: 59.4, 77.1]). In NPH mice, NP cells were detected in paravertebral tissue (38.6 [32.0, 45.2]) and draining lymph nodes (dLN) at 4 h (76.9 [54.9, 98.8]). A significant increase of NP cells in dLNs was observed at 24 h (157.1 [113.7, 200.6]). Most of the herniated NP cells were cleared in paravertebral tissue after 1 week (7.5 [4.4, 10.6]), but disc inflammation peaked at 1 week (19.9% [14.7, 25.1]), along with persistent lymphangiogenesis (9.5 [7.2, 11.8]). However, conditional Vegfr3 knockout mice exhibited impaired lymphangiogenesis (5.7 [4.4, 7.0]) and herniated NP cell clearance (6.1 [1.8, 10.5]) during NPH, leading to exacerbated disc inflammation (23.7% [19.3, 28.2]).

CONCLUSION

The paravertebral lymphatic system is involved in the NPH resorption and inflammation regression. Promoting lymphangiogenesis may be a novel strategy for facilitating NPH resorption and inflammation regression in patients with LDH.

Multiscale computational analysis of the steady fluid flow through a lymph node

Lymph Nodes (LNs) are crucial to the immune and lymphatic systems, filtering harmful substances and regulating lymph transport. LNs consist of a lymphoid compartment (LC) that forms a porous bulk region, and a subcapsular sinus (SCS), which is a free-fluid region. Mathematical and mechanical challenges arise in understanding lymph flow dynamics. The highly vascularized lymph node connects the lymphatic and blood systems, emphasizing its essential role in maintaining the fluid balance in the body. In this work, we describe a mathematical model in a steady setting to describe the lymph transport in a lymph node. We couple the fluid flow in the SCS governed by an incompressible Stokes equation with the fluid flow in LC, described by a model obtained by means of asymptotic homogenisation technique, taking into account the multiscale nature of the node and the fluid exchange with the blood vessels inside it. We solve this model using numerical simulations and we analyze the lymph transport inside the node to elucidate its regulatory mechanisms and significance. Our results highlight the crucial role of the microstructure of the lymph node in regularising its fluid balance. These results can pave the way to a better understanding of the mechanisms underlying the lymph node's multiscale functionalities which can be significantly affected by specific physiological and pathological conditions, such as those characterising malignant tissues.

Effects of Postoperative Oral Corticosteroids on Infection Rates in Upper Extremity Surgery

BACKGROUND

The recent trend in administering postoperative oral corticosteroids has proven effective in alleviating pain and improving surgical outcomes for hand and upper extremity procedures. However, concerns persist regarding potential infection risks despite a lack of supporting evidence in the current literature. We propose that a 6-day regimen of low-dose postoperative oral corticosteroids is safe and does not increase the likelihood of surgical site infections (SSIs) in adult upper extremity surgeries.

METHODS

A retrospective study of all adult patients who underwent clean, upper extremity surgery, including both soft tissue and hardware implantation cases, between November 2021 and November 2023, performed at a single institution were included in the study. Primary outcome measures were diagnosis of SSI by 14 days and 30 days. Categorical variables were compared using χ2 tests, and continuous variables were compared using Wilcoxon rank-sum tests. A P value less than .05 was considered statistically significant.

RESULTS

A total of 813 cases were included for analysis-196 received a 6-day course of postoperative oral steroids (methylprednisolone) and 617 did not. Both groups had similar SSI rates of 4.1% and 3.1%, respectively, with no statistical differences between the groups at any postoperative time. Subgroup analysis of patients diagnosed with an SSI identified no statistically different demographic factors or medical comorbidities when comparing patients who received postoperative oral corticosteroids versus those who did not.

CONCLUSIONS

Low-dose, postoperative oral steroid use following adult upper extremity surgery is safe and does not increase the risk of SSI. Further investigations with prospective studies on postoperative oral corticosteroids would prove advantageous.

The role of ferroptosis resistance in lymph-associated tumour metastasis

Tumour metastasis is a crucial factor in determining clinically challenging tumours. In this respect, the lymphatic system may act as potential entry portals for tumour metastasis, whilst, clinical detection of tumour-infiltrated lymph nodes also indicates poorer prognosis and higher metastatic risk. Whether tumour cells gain ferroptosis resistance in lymph that make them exhibit a stronger propensity for lymphatic dissemination compared to hematogenous spread might be a breakthrough for elucidating lymph-associated tumour metastasis. This review discusses how the lymphatic system endows tumour cells with ferroptosis resistance character, which makes them more propensity for lymph node pre-metastasis and distant metastasis through lymphatic circulation. Comprehensively considering the distinct structure and property of lymph and the unique metabolic characteristics of tumours, all of the lymphatic vessels, intestinal lymph and lymph nodes collectively manipulate an intricate interaction with the hematogenous system and afford substances exchange with tumour cells and extracellular vesicles, upon which make a ferroptosis resistant microenvironment for subsequent metastasis in distant organs and lymph nodes.

Investigations on the Hemostatic Potential of Physiological Body Fluids

Current blood coagulation models consider the interactions between blood, the vessel wall, and other tissues that expose tissue factor (TF), the main initiator of coagulation. A potential role of body fluids other than blood is generally not considered. In this review, we summarize the evidence that body fluids such as mother's milk saliva, urine, semen, and amniotic fluid trigger coagulation. The ability of these body fluids to trigger coagulation is explained by the presence of extracellular vesicles (EVs). These EVs expose extrinsic tenase complexes (i.e., complexes of TF and activated factor VII) that can trigger coagulation. Why these body fluids share this activity, however, is unknown. Possible explanations are that these body fluids contribute to hemostatic protection and/or to the regulation of the epithelial barrier function. Further investigations may help understand the underlying cellular and biochemical pathways regulating or contributing to coagulation and innate immunity, which may be directly relevant to medical conditions such as gastrointestinal bleeding and chronic inflammatory bowel disease.

Restoration of cervical lymphatic vessel function in aging rescues cerebrospinal fluid drainage

Cervical lymphatic vessels (cLVs) have been shown to drain solutes and cerebrospinal fluid (CSF) from the brain. However, their hydrodynamical properties have never been evaluated in vivo. Here, we developed two-photon optical imaging with particle tracking in vivo of CSF tracers (2P-OPTIC) in superficial and deep cLVs of mice, characterizing their flow and showing that the major driver is intrinsic pumping by contraction of the lymphatic vessel wall. Moreover, contraction frequency and flow velocity were reduced in aged mice, which coincided with a reduction in smooth muscle actin expression. Slowed flow in aged mice was rescued using topical application of prostaglandin F2α, a prostanoid that increases smooth muscle contractility, which restored lymphatic function in aged mice and enhanced central nervous system clearance. We show that cLVs are important regulators of CSF drainage and that restoring their function is an effective therapy for improving clearance in aging.

Lymphangiogenesis: novel strategies to promote cutaneous wound healing

The cutaneous lymphatic system regulates tissue inflammation, fluid balance and immunological responses. Lymphangiogenesis or lymphatic dysfunction may lead to lymphedema, immune deficiency, chronic inflammation etc. Tissue regeneration and healing depend on angiogenesis and lymphangiogenesis during wound healing. Tissue oedema and chronic inflammation can slow wound healing due to impaired lymphangiogenesis or lymphatic dysfunction. For example, impaired lymphangiogenesis or lymphatic dysfunction has been detected in nonhealing wounds such as diabetic ulcers, venous ulcers and bedsores. This review summarizes the structure and function of the cutaneous lymphatic vessel system and lymphangiogenesis in wounds. Furthermore, we review wound lymphangiogenesis processes and remodelling, especially the influence of the inflammatory phase. Finally, we outline how to control lymphangiogenesis to promote wound healing, assess the possibility of targeting lymphangiogenesis as a novel treatment strategy for chronic wounds and provide an analysis of the possible problems that need to be addressed.

Biomarkers of lymph node metastasis in colorectal cancer: update

Colorectal cancer (CRC) ranks as the second leading cause of cancer-related deaths globally, trailing only behind lung cancer, and stands as the third most prevalent malignant tumor, following lung and breast cancers. The primary cause of mortality in colorectal cancer (CRC) stems from distant metastasis. Among the various routes of metastasis in CRC, lymph node metastasis predominates, serving as a pivotal factor in both prognostication and treatment decisions for patients. This intricate cascade of events involves multifaceted molecular mechanisms, highlighting the complexity underlying lymph node metastasis in CRC. The cytokines or proteins involved in lymph node metastasis may represent the most promising lymph node metastasis markers for clinical use. In this review, we aim to consolidate the current understanding of the mechanisms and pathophysiology underlying lymph node metastasis in colorectal cancer (CRC), drawing upon insights from the most recent literatures. We also provide an overview of the latest advancements in comprehending the molecular underpinnings of lymph node metastasis in CRC, along with the potential of innovative targeted therapies. These advancements hold promise for enhancing the prognosis of CRC patients by addressing the challenges posed by lymph node metastasis.

A quasilinear hyperbolic one-dimensional model of the lymph flow through a lymphangion with valve dynamics and a contractile wall

This paper presents a one-dimensional model that describes fluid flow in lymphangions, the segments of lymphatic vessels between valves, using quasilinear hyperbolic systems. The model incorporates a phenomenological pressure-cross-sectional area relationship based on existing literature. Numerical solutions of the differential equations align with known results, offering insights into lymphatic flow dynamics. This model enhances the understanding of lymph movement through the lymphatic system, driven by lymphangion contractions.

The Lymphatic Vascular System: Does Nonuniform Lymphangion Length Limit Flow-Rate?

A previously developed model of a lymphatic vessel as a chain of lymphangions was investigated to determine whether lymphangions of unequal length reduce pumping relative to a similar chain of equal-length ones. The model incorporates passive elastic and active contractile properties taken from ex vivo measurements, and intravascular lymphatic valves as transvalvular pressure-dependent resistances to flow with hysteresis and transmural pressure-dependent bias to the open state as observed experimentally. Coordination of lymphangion contractions is managed by marrying an autonomous transmural pressure-dependent pacemaker for each lymphangion with bidirectional transmission of activation signals between lymphangions, qualitatively matching empirical observations. With eight lymphangions as used here and many nonlinear constraints, the model is capable of complex outcomes. The expected flow-rate advantage conferred by longer lymphangions everywhere was confirmed. However, the anticipated advantage of uniform lymphangions over those of unequal length, compared in chains of equal overall length, was not found. A wide variety of dynamical outcomes was observed, with the most powerful determinant being the adverse pressure difference, rather than the arrangement of long and short lymphangions. This work suggests that the wide variation in lymphangion length which is commonly observed in collecting lymphatic vessels does not confer disadvantage in pumping lymph.

Understanding lymphatic drug delivery through chylomicron blockade: A retrospective and prospective analysis

Scientists have developed and employed various models to investigate intestinal lymphatic uptake. One approach involves using specific blocking agents to influence the chylomicron-mediated lymphatic absorption of drugs. Currently utilized models include pluronic L-81, puromycin, vinca alkaloids, colchicine, and cycloheximide. This review offers a thorough analysis of the diverse models utilized, evaluating existing reports while delineating the gaps in current research. It also explores pharmacokinetic related aspects of intestinal lymphatic uptake pathway and its blockage through the discussed models. Pluronic L-81 has a reversible effect, minimal toxicity, and unique mode of action. Yet, it lacks clinical reports on chylomicron pathway blockage, likely due to low concentrations used. Puromycin and vinca alkaloids, though documented for toxicity, lack information on their application in drug intestinal lymphatic uptake. Other vinca alkaloids show promise in affecting triglyceride profiles and represent possible agents to test as blockers. Colchicine and cycloheximide, widely used in pharmaceutical development, have demonstrated efficacy, with cycloheximide preferred for lower toxicity. However, further investigation into effective and toxic doses of colchicine in humans is needed to understand its clinical impact. The review additionally followed the complete journey of oral lymphatic targeting drugs from intake to excretion, provided a pharmacokinetic equation considering the intestinal lymphatic pathway for assessing bioavailability. Moreover, the possible application of urinary data as a non-invasive way to measure the uptake of drugs through intestinal lymphatics was illustrated, and the likelihood of drug interactions when specific blockers are employed in human subjects was underscored.

A multi-scale numerical study of monoclonal antibodies uptake by initial lymphatics after subcutaneous injection

This paper studies the transport of monoclonal antibodies through skin tissue and initial lymphatics, which impacts the pharmacokinetics of monoclonal antibodies. Our model integrates a macroscale representation of the entire skin tissue with a mesoscale model that focuses on the papillary dermis layer. Our results indicate that it takes hours for the drugs to disperse from the injection site to the papillary dermis before entering the initial lymphatics. Additionally, we observe an inhomogeneous drug distribution in the interstitial space of the papillary dermis, with higher drug concentrations near initial lymphatics and lower concentrations near blood capillaries. To validate our model, we compare our numerical simulation results with experimental data, finding a good alignment. Our parametric studies on the drug molecule properties and injection parameters suggest that a higher diffusion coefficient increases the transport and uptake rate while binding slows down these processes. Furthermore, shallower injection depths lead to faster lymphatic uptake, whereas the size of the injection plume has a minor effect on the uptake rate. These findings advance our understanding of drug transport and lymphatic absorption after subcutaneous injection, offering valuable insights for optimizing drug delivery strategies and the design of biotherapeutics.

Fluid-Dynamic Modeling of Flow in Embryonic Tissue Indicates That Lymphatic Valve Location Is Not Consistently Determined by the Local Fluid Shear or Its Gradient

OBJECTIVE

Intravascular lymphatic valves often occur in proximity to vessel junctions. It is commonly held that disturbed flow at junctions is responsible for accumulation of valve-forming cells (VFCs) at these locations as the initial step in valve creation, and the one which explains the association with these sites. However, evidence in favor is largely limited to cell culture experiments.

METHODS

We acquired images of embryonic lymphatic vascular networks from day E16.5, when VFC accumulation has started but the developing valve has not yet altered the local vessel geometry, stained for Prox1, which co-localizes with Foxc2. Using finite-element computational fluid mechanics, we simulated the flow through the networks, under conditions appropriate to this early development stage. Then we correlated the Prox1 distributions with the distributions of simulated fluid shear and shear stress gradient.

RESULTS

Across a total of 16 image sets, no consistent correlation was found between Prox1 distribution and the local magnitude of fluid shear, or its positive or negative gradient.

CONCLUSIONS

This, the first direct semi-empirical test of the localization hypothesis to interrogate the tissue from in vivo at the critical moment of development, does not support the idea that a feature of the local flow determines valve localization.

Dosing Adjustments in Cases of Altered Plasma Protein Binding are Most Needed for Drugs with a Volume of Distribution Below 1.3 L/kg

BACKGROUND

The present literature offers conflicting views on the importance of changes in plasma protein binding in clinical therapeutics. Furthermore, there are no methods to calculate a new dosing regimen when such changes occur.

METHODS

Previous models developed by Balaz et al. and Greenblat et al. were used to calculate a plasma protein binding (PPB) score for individual drugs based on the volume of distribution for total concentration and the bound fraction of drug. The models were further used to calculate a new drug dosing interval for cases of altered plasma protein binding. The equations apply best for drugs with fast absorption and fast distribution; they can be used as approximations for drugs with slow distribution by using the volume of distribution at steady state and the rate constant of the elimination phase.

RESULTS

The newly developed equations show that changes in plasma protein binding are relevant only for drugs with a positive PPB score; such drugs must have a volume of distribution for total concentration below 1.3 L/kg and high protein binding. It is further shown that the drug dosing interval should be reduced when the remaining fraction of plasma protein binding is below the PPB score.

CONCLUSION

A new method to rank drugs according to the impact of changes in plasma protein binding on their pharmacokinetic profile was developed. The new method was applied to show that drugs with high PPB scores need reductions in their dosing interval when the level of protein binding decreases.

Modelling the innate immune system in microphysiological systems

This critical review aims to highlight how modeling of the immune response has adapted over time to utilize microphysiological systems. Topics covered here will discuss the integral components of the immune system in various human body systems, and how these interactions are modeled using these systems. Through the use of microphysiological systems, we have not only expanded on foundations of basic immune cell information, but have also gleaned insight on how immune cells work both independently and collaboratively within an entire human body system.

Numerical investigation on flow-induced wall shear stress variation of metastatic cancer cells in lymphatics with elastic valves

Hematogenous metastasis occurs when cancer cells detach from the extracellular matrix in the primary tumor into the bloodstream or lymphatic system. Elucidating the response of metastatic tumor cells in suspension to the flow conditions in lymphatics with valves from a mechanical/fluidic perspective is necessary. A physiologically relevant computational model of a lymphatic vessel with valves was constructed using fully coupled fluid-cell-vessel interactions to investigate the effects of lymphatic vessel contractility, valve properties, and cell size and stiffness on the variations in magnitude and gradient of the flow-induced wall shear stress (WSS) experienced by suspended tumor cells. Results indicated that the maximum WSSmax increased with the increments in cell diameter, vessel contraction amplitude, and valve stiffness. The decrease in vessel contraction period and valve aspect ratio also increased the maximum WSSmax. The influence of the properties of the valve on the WSS was more significant among the factors mentioned above. The maximum WSSmax acting on the cancer cell when the cell reversed the direction of its motion in the valve region increased by 0.5-1.4 times that before the cell entered the valve region. The maximum change in WSS was in the range of 0.004-0.028 Pa/µm depending on the factors studied. They slightly exceeded the values associated with breast cancer cell apoptosis. The results of this study provide biofluid mechanics-based support for mechanobiological research on the metastasis of metastatic cancer cells in suspension within the lymphatics.

Molecular pathophysiology of secondary lymphedema

Lymphedema occurs as a result of lymphatic vessel damage or obstruction, leading to the lymphatic fluid stasis, which triggers inflammation, tissue fibrosis, and adipose tissue deposition with adipocyte hypertrophy. The treatment of lymphedema is divided into conservative and surgical approaches. Among surgical treatments, methods like lymphaticovenular anastomosis and vascularized lymph node transfer are gaining attention as they focus on restoring lymphatic flow, constituting a physiologic treatment approach. Lymphatic endothelial cells form the structure of lymphatic vessels. These cells possess button-like junctions that facilitate the influx of fluid and leukocytes. Approximately 10% of interstitial fluid is connected to venous return through lymphatic capillaries. Damage to lymphatic vessels leads to lymphatic fluid stasis, resulting in the clinical condition of lymphedema through three mechanisms: Inflammation involving CD4+ T cells as the principal contributing factor, along with the effects of immune cells on the VEGF-C/VEGFR axis, consequently resulting in abnormal lymphangiogenesis; adipocyte hypertrophy and adipose tissue deposition regulated by the interaction of CCAAT/enhancer-binding protein α and peroxisome proliferator-activated receptor-γ; and tissue fibrosis initiated by the overactivity of Th2 cells, leading to the secretion of profibrotic cytokines such as IL-4, IL-13, and the growth factor TGF-β1. Surgical treatments aimed at reconstructing the lymphatic system help facilitate lymphatic fluid drainage, but their effectiveness in treating already damaged lymphatic vessels is limited. Therefore, reviewing the pathophysiology and molecular mechanisms of lymphedema is crucial to complement surgical treatments and explore novel therapeutic approaches.

Multiscale homogenization for dual porosity time-dependent Darcy-Brinkman/Darcy coupling and its application to the lymph node

We study the coupling between time-dependent Darcy-Brinkman and the Darcy equations at the microscale subjected to inhomogeneous body forces and initial conditions to describe a double porosity problem. We derive the homogenized governing equations for this problem using the asymptotic homogenization technique, and as macroscopic results, we obtain a coupling between two Darcy equations, one of which with memory effects, with mass exchange between phases. The memory effects are a consequence of considering the time dependence in the Darcy-Brinkman equation, and they allow us to study in more detail the role of time in the problem under consideration. After the formulation of the model, we solve it in a simplified setting and we use it to describe the movement of fluid within a vascularized lymph node.

Lymphatic uptake of the lipidated and non-lipidated GLP-1 agonists liraglutide and exenatide is similar in rats

Peptides, despite their therapeutic potential, face challenges with undesirable pharmacokinetic (PK) properties and biodistribution, including poor oral absorption and cellular uptake, and short plasma elimination half-lives. Lipidation of peptides is a common strategy to improve their physicochemical and PK properties, making them viable drug candidates. For example, the plasma half-life of peptides has been extended via conjugation to lipids that are proposed to promote binding to serum albumin and thus protect against rapid clearance. Recent work has shown that lipid conjugation to oligodeoxynucleotides, polymers and small molecule drugs results in association not only with albumin, but also with lipoproteins, resulting in half-life prolongation and transport from administration sites via the lymphatics. Enhancing delivery into the lymph increases the efficacy of vaccines and therapeutics with lymphatic targets such as immunotherapies. In this study, the plasma PK, lymphatic uptake, and bioavailability of the glucagon-like peptide-1 (GLP-1) receptor agonist peptides, liraglutide (lipidated) and exenatide (non-lipidated), were investigated following subcutaneous (SC) administration to rats. As expected, liraglutide displayed an apparent prolonged plasma half-life (9.1 versus 1 h), delayed peak plasma concentrations and lower bioavailability (∼10 % versus ∼100 %) compared to exenatide after SC administration. The lymphatic uptake of both peptides was relatively low (<0.5 % of the dose) although lymph to plasma concentration ratios were greater than one for several early timepoints suggesting some direct uptake into lymph. The low lymphatic uptake may be due to the nature of the conjugated lipid (a single-chain C16 palmitic acid in liraglutide) but suggests that other peptides with similar lipid conjugations may also have relatively modest lymphatic uptake. If delivery to the lymph is desired, conjugation to more lipophilic moieties with higher albumin and/or lipoprotein binding efficiencies, such as diacylglycerols, may be appropriate.

Single-cell topographical profiling of the immune synapse reveals a biomechanical signature of cytotoxicity

Immune cells have intensely physical lifestyles characterized by structural plasticity and force exertion. To investigate whether specific immune functions require stereotyped mechanical outputs, we used super-resolution traction force microscopy to compare the immune synapses formed by cytotoxic T cells with contacts formed by other T cell subsets and by macrophages. T cell synapses were globally compressive, which was fundamentally different from the pulling and pinching associated with macrophage phagocytosis. Spectral decomposition of force exertion patterns from each cell type linked cytotoxicity to compressive strength, local protrusiveness, and the induction of complex, asymmetric topography. These features were validated as cytotoxic drivers by genetic disruption of cytoskeletal regulators, live imaging of synaptic secretion, and in silico analysis of interfacial distortion. Synapse architecture and force exertion were sensitive to target stiffness and size, suggesting that the mechanical potentiation of killing is biophysically adaptive. We conclude that cellular cytotoxicity and, by implication, other effector responses are supported by specialized patterns of efferent force.

Lymphatic failure and lymphatic interventions: Knowledge gaps and future directions for a new frontier in congenital heart disease

Lymphatic failure is a broad term that describes the lymphatic circulation's inability to adequately transport fluid and solutes out of the interstitium and into the systemic venous circulation, which can result in dysfunction and dysregulation of immune responses, dietary fat absorption, and fluid balance maintenance. Several investigations have recently elucidated the nexus between lymphatic failure and congenital heart disease, and the associated morbidity and mortality is now well-recognized. However, the precise pathophysiology and pathogenesis of lymphatic failure remains poorly understood and relatively understudied, and there are no targeted therapeutics or interventions to reliably prevent its development and progression. Thus, there is growing enthusiasm towards the development and application of novel percutaneous and surgical lymphatic interventions. Moreover, there is consensus that further investigations are needed to delineate the underlying mechanisms of lymphatic failure, which could help identify novel therapeutic targets and develop innovative procedures to improve the overall quality of life and survival of these patients. With these considerations, this review aims to provide an overview of the lymphatic circulation and its vasculature as it relates to current understandings into the pathophysiology and pathogenesis of lymphatic failure in patients with congenital heart disease, while also summarizing strategies for evaluating and managing lymphatic complications, as well as specific areas of interest for future translational and clinical research efforts.

Genetic causes of lymphatic disorders: recent updates on the clinical and molecular aspects of lymphatic disease

PURPOSE OF REVIEW

The lymphatic system facilitates several key functions that limit significant morbidity and mortality. Despite the impact and burden of lymphatic disorders, there are many remaining disorders whose genetic substrate remains unknown. The purpose of this review is to provide an update on the genetic causes of lymphatic disorders, while reporting on newly proposed clinical classifications of lymphatic disease.

RECENT FINDINGS

We reviewed several new mutations in genes that have been identified as potential causes of lymphatic disorders including: MDFIC, EPHB 4 , and ANGPT2. Furthermore, the traditional St. George's Classification system for primary lymphatic anomalies has been updated to reflect the use of genetic testing, both as a tool for the clinical identification of lymphatic disease and as a method through which new sub-classifications of lymphatic disorders have been established within this framework. Finally, we highlighted recent clinical studies that have explored the impact of therapies such as sirolimus, ketoprofen, and acebilustat on lymphatic disorders.

SUMMARY

Despite a growing body of evidence, current literature demonstrates a persistent gap in the number of known genes responsible for lymphatic disease entities. Recent clinical classification tools have been introduced in order to integrate traditional symptom- and time-based diagnostic approaches with modern genetic classifications, as highlighted in the updated St. George's classification system. With the introduction of this novel approach, clinicians may be better equipped to recognize established disease and, potentially, to identify novel causal mutations. Further research is needed to identify additional genetic causes of disease and to optimize current clinical tools for diagnosis and treatment.

Mimicking blood and lymphatic vasculatures using microfluidic systems

The role of the circulatory system, containing the blood and lymphatic vasculatures, within the body, has become increasingly focused on by researchers as dysfunction of either of the systems has been linked to serious complications and disease. Currently, in vivo models are unable to provide the sufficient monitoring and level of manipulation needed to characterize the fluidic dynamics of the microcirculation in blood and lymphatic vessels; thus in vitro models have been pursued as an alternative model. Microfluidic devices have the required properties to provide a physiologically relevant circulatory system model for research as well as the experimental tools to conduct more advanced research analyses of microcirculation flow. In this review paper, the physiological behavior of fluid flow and electrical communication within the endothelial cells of the systems are detailed and discussed to highlight their complexities. Cell co-culturing methods and other relevant organ-on-a-chip devices will be evaluated to demonstrate the feasibility and relevance of the in vitro microfluidic model. Microfluidic systems will be determined as a noteworthy model that can display physiologically relevant flow of the cardiovascular and lymphatic systems, which will enable researchers to investigate the systems' prevalence in diseases and identify potential therapeutics.

Minimal Determinants for Lifelong Antiviral Antibody Responses in Mice from a Single Exposure to Virus-like Immunogens at Low Doses

The durability of an antibody (Ab) response is highly important for antiviral vaccines. However, due to the complex compositions of natural virions, the molecular determinants of Ab durability from viral infection or inactivated viral vaccines have been incompletely understood. Here we used a reductionist system of liposome-based virus-like structures to examine the durability of Abs from primary immune responses in mice. This system allowed us to independently vary fundamental viral attributes and to do so without additional adjuvants to model natural viruses. We show that a single injection of protein antigens (Ags) orderly displayed on a virion-sized liposome is sufficient to induce a long-lived neutralizing Ab (nAb) response. The introduction of internal nucleic acids dramatically modulates the magnitude of Ab responses without an alteration of the long-term kinetic trends. These Abs are characterized by very slow off-rates of ~0.0005 s-1, which emerged as early as day 5 after injection and these off-rates are comparable to that of affinity-matured monoclonal Abs. A single injection of these structures at doses as low as 100 ng led to lifelong nAb production in mice. Thus, a minimal virus-like immunogen can give rise to potent and long-lasting antiviral Abs in a primary response in mice without live infection. This has important implications for understanding both live viral infection and for optimizing vaccine design.

The Role of Inflammation in Lymphedema: A Narrative Review of Pathogenesis and Opportunities for Therapeutic Intervention

Lymphedema is a chronic and progressive disease of the lymphatic system characterized by inflammation, increased adipose deposition, and tissue fibrosis. Despite early hypotheses identifying lymphedema as a disease of mechanical lymphatic disruption alone, the progressive inflammatory nature underlying this condition is now well-established. In this review, we provide an overview of the various inflammatory mechanisms that characterize lymphedema development and progression. These mechanisms contribute to the acute and chronic phases of lymphedema, which manifest clinically as inflammation, fibrosis, and adiposity. Furthermore, we highlight the interplay between current therapeutic modalities and the underlying inflammatory microenvironment, as well as opportunities for future therapeutic development.

The follicular lymphoma tumor microenvironment at single-cell and spatial resolution

ABSTRACT

Follicular lymphoma (FL) is a generally incurable malignancy that originates from developmentally blocked germinal center B cells residing, primarily, within lymph nodes (LNs). During the long natural history of FL, malignant B cells often disseminate to multiple LNs and can affect virtually any organ. Nonmalignant LNs are highly organized structures distributed throughout the body, in which they perform functions critical for host defense. In FL, the malignant B cells "re-educate" the lymphoid environment by altering the phenotype, distribution, and abundance of other cells such as T cells, macrophages, and subsets of stromal cells. Consequently, dramatic anatomical changes occur and include alterations in the number, shape, and size of neoplastic follicles with an accompanying attenuation of the T-cell zone. Ongoing and dynamic interactions between FL B cells and the tumor microenvironment (TME) result in significant clinical heterogeneity observed both within and across patients. Over time, FL evolves into pathological variants associated with distinct outcomes, ranging from an indolent disease to more aggressive clinical courses with early death. Given the importance of both cell-intrinsic and -extrinsic factors in shaping disease progression and patient survival, comprehensive examination of FL tumors is critical. Here, we describe the cellular composition and architecture of normal and malignant human LNs and provide a broad overview of emerging technologies for deconstructing the FL TME at single-cell and spatial resolution. We additionally discuss the importance of capturing samples at landmark time points as well as longitudinally for clinical decision-making.

Nitric Oxide‐Based Nanomedicines for Conquering TME Fortress: Say “NO” to Insufficient Tumor Treatment

Almost all cancer treatments are significantly limited by the strong tumor microenvironment (TME) fortress formed by abnormal vasculature, dense extracellular matrix (ECM), multidrug resistance (MDR) system, and immune “cold” environment. In the huge efforts of dismantling the TME fortress, nitric oxide (NO)‐based nanomedicines are increasingly occupying a central position and have already been identified as super “strong polygonal warriors” to dismantle TME fortress for efficient cancer treatment, benefiting from NO's unique physicochemical properties and extremely fascinating biological effects. However, there is a paucity of systematic review to elaborate on the progress and fundamental mechanism of NO‐based nanomedicines in oncology from this aspect. Herein, the key characteristics of TME fortress and the potential of NO in reprogramming TME are delineated and highlighted. The evolution of NO donors and the advantages of NO‐based nanomedicines are discussed subsequently. Moreover, the latest progress of NO‐based nanomedicines for solid tumors is comprehensively reviewed, including normalizing tumor vasculature, overcoming ECM barrier, reversing MDR, and reactivating the immunosuppression TME. Lastly, the prospects, limitations, and future directions on NO‐based nanomedicines for TME manipulation are discussed to provide new insights into the construction of more applicable anticancer nanomedicines.

Mechanisms of Myocardial Edema Development in CVD Pathophysiology

Myocardial edema is the excess accumulation of fluid in the myocardial interstitium or cardiac cells that develops due to changes in capillary permeability, loss of glycocalyx charge, imbalance in lymphatic drainage, or a combination of these factors. Today it is believed that this condition is not only a complication of cardiovascular diseases, but in itself causes aggravation of the disease and increases the risks of adverse outcomes. The study of molecular, genetic, and mechanical changes in the myocardium during edema may contribute to the development of new approaches to the diagnosis and treatment of this condition. This review was conducted to describe the main mechanisms of myocardial edema development at the molecular and cellular levels and to identify promising targets for the regulation of this condition based on articles cited in Pubmed up to January 2024.

Sleep disorders and Alzheimer's disease pathophysiology: The role of the Glymphatic System. A scoping review

BACKGROUND

Alzheimer's disease (AD) is highly intertwined with sleep disturbances throughout its whole natural history. Sleep consists of a major compound of the functionality of the glymphatic system, as the synchronized slow-wave activity during NREM facilitates cerebrospinal and interstitial long-distance mixing.

OBJECTIVE

The present study undertakes a scoping review of research on the involvement of the glymphatic system in AD-related sleep disturbances.

DESIGN

we searched Medline, Embase, PsychInfo and HEAL-link databases, without limitations on date and language, along with reference lists of relevant reviews and all included studies. We included in vivo, in vitro and post-mortem studies examining glymphatic implications of sleep disturbances in human populations with AD spectrum pathology. A thematic synthesis of evidence based on the extracted content was applied and presented in a narrative way.

RESULTS

In total, 70 original research articles were included and were grouped as following: a) Protein aggregation and toxicity, after sleep deprivation, along with its effects on sleep architecture, b) Glymphatic Sequalae in SDB, yielding potential glymphatic markers c) Circadian Dysregulation, d) Possible Interventions.

CONCLUSIONS

this review sought to provide insight into the role of sleep disturbances in AD pathogenesis, in the context of the glymphatic disruption.

MR Lymphangiography in Lymphatic Disorders: Clinical Applications, Institutional Experience, and Practice Development

Lymphatic flow and anatomy can be challenging to study, owing to variable lymphatic anatomy in patients with diverse primary or secondary lymphatic pathologic conditions and the fact that lymphatic imaging is rarely performed in healthy individuals. The primary components of the lymphatic system outside the head and neck are the peripheral, retroperitoneal, mesenteric, hepatic, and pulmonary lymphatic systems and the thoracic duct. Multiple techniques have been developed for imaging components of the lymphatic system over the past century, with trade-offs in spatial, temporal, and contrast resolution; invasiveness; exposure to ionizing radiation; and the ability to obtain information on dynamic lymphatic flow. More recently, dynamic contrast-enhanced (DCE) MR lymphangiography (MRL) has emerged as a valuable tool for imaging both lymphatic flow and anatomy in a variety of congenital and acquired primary or secondary lymphatic disorders. The authors provide a brief overview of lymphatic physiology, anatomy, and imaging techniques. Next, an overview of DCE MRL and the development of an MRL practice and workflow in a hybrid interventional MRI suite incorporating cart-based in-room US is provided, with an emphasis on multidisciplinary collaboration. The spectrum of congenital and acquired lymphatic disorders encountered early in an MRL practice is provided, with emphasis on the diversity of imaging findings and how DCE MRL can aid in diagnosis and treatment of these patients. Methods such as DCE MRL for assessing the hepatic and mesenteric lymphatic systems and emerging technologies that may further expand DCE MRL use such as three-dimensional printing are introduced. ©RSNA, 2024 Test Your Knowledge questions for this article are available in the supplemental material.

Hydroxymethylnitrofurazone lymphatic uptake with nanostructured lipid carrier after oral administration in rats

Background: Leishmaniasis, caused by the protozoan Leishmania sp., infects phagocyte cells present in lymphatic organs. This study demonstrates the influence of nanostructured lipid carrier-loaded hydroxymethylnitrofurazone (NLC-NFOH) on lymphatic uptake using a chylomicron-blocking flow model in rats. Method: Lymphatic uptake of NFOH was assessed 1 h after oral administration of dimethyl sulfoxide with NFOH or NLC-NFOH with and without cycloheximide pretreatment. Result: Dimethyl sulfoxide with NFOH and NLC-NFOH showed NFOH serum concentrations of 0.0316 and 0.0291 μg/ml, respectively. After chylomicron blocking, NFOH was not detected. Conclusion: Despite log P below 5, NFOH was successfully taken up by the lymphatic system. Long-chain fatty acids and particle size might be main factors in these findings. NLC-NFOH is a promising and convenient platform for treating leishmaniasis via oral administration.

Flow-dependent regulation of rat mesenteric lymphatic vessel contractile response requires activation of endothelial TRPV4 channels

OBJECTIVES

The objective of our study is to evaluate the involvement of the transient receptor potential vanilloid 4 (TRPV4) in the alteration of lymphatic pumping in response to flow and determine the signaling pathways involved.

METHODS

We used immunofluorescence imaging and western blotting to assess TRPV4 expression in rat mesenteric lymphatic vessels. We examined inhibition of TRPV4 with HC067047, nitric oxide synthase (NOS) with L-NNA and cyclooxygenases (COXs) with indomethacin on the contractile response of pressurized lymphatic vessels to flow changes induced by a stepwise increase in pressure gradients, and the functionality of endothelial TRPV4 channels by measuring the intracellular Ca2+ response of primary lymphatic endothelial cell cultures to the selective agonist GSK1016790A.

RESULTS

TRPV4 protein was expressed in both the endothelial and the smooth muscle layer of rat mesenteric lymphatics with high endothelial expression around the valve sites. When maintained under constant transmural pressure, most lymphatic vessels displayed a decrease in contraction frequency under conditions of flow and this effect was ablated through inhibition of NOS, COX or TRPV4.

CONCLUSIONS

Our findings demonstrate a critical role for TRPV4 in the decrease in contraction frequency induced in lymphatic vessels by increases in flow rate via the production and action of nitric oxide and dilatory prostanoids.

Microfluidic-Based Reconstitution of Functional Lymphatic Microvasculature: Elucidating the Role of Lymphatics in Health and Disease

The knowledge of the blood microvasculature and its functional role in health and disease has grown significantly attributable to decades of research and numerous advances in cell biology and tissue engineering; however, the lymphatics (the secondary vascular system) has not garnered similar attention, in part due to a lack of relevant in vitro models that mimic its pathophysiological functions. Here, a microfluidic-based approach is adopted to achieve precise control over the biological transport of growth factors and interstitial flow that drive the in vivo growth of lymphatic capillaries (lymphangiogenesis). The engineered on-chip lymphatics with in vivo-like morphology exhibit tissue-scale functionality with drainage rates of interstitial proteins and molecules comparable to in vivo standards. Computational and scaling analyses of the underlying transport phenomena elucidate the critical role of the three-dimensional geometry and lymphatic endothelium in recapitulating physiological drainage. Finally, the engineered on-chip lymphatics enabled studies of lymphatic-immune interactions that revealed inflammation-driven responses by the lymphatics to recruit immune cells via chemotactic signals similar to in vivo, pathological events. This on-chip lymphatics platform permits the interrogation of various lymphatic biological functions, as well as screening of lymphatic-based therapies such as interstitial absorption of protein therapeutics and lymphatic immunomodulation for cancer therapy.

Computational fluid dynamic modeling of the lymphatic system: a review of existing models and future directions

Historically, research into the lymphatic system has been overlooked due to both a lack of knowledge and limited recognition of its importance. In the last decade however, lymphatic research has gained substantial momentum and has included the development of a variety of computational models to aid understanding of this complex system. This article reviews existing computational fluid dynamic models of the lymphatics covering each structural component including the initial lymphatics, pre-collecting and collecting vessels, and lymph nodes. This is followed by a summary of limitations and gaps in existing computational models and reasons that development in this field has been hindered to date. Over the next decade, efforts to further characterize lymphatic anatomy and physiology are anticipated to provide key data to further inform and validate lymphatic fluid dynamic models. Development of more comprehensive multiscale- and multi-physics computational models has the potential to significantly enhance the understanding of lymphatic function in both health and disease.

A compartment model for subcutaneous injection of monoclonal antibodies

Despite the growing popularity of subcutaneous (SC) administration for monoclonal antibodies (mAbs), there remains a limited understanding of the significance of mAb transport rate constants within the interstitial space and the lymphatic system on their pharmacokinetics. To bridge this knowledge gap, we introduce a compartmental model for subcutaneously administered mAbs. Our model differentiates FcRn-expressing cells across various sites, and the model predictions agree with experimental data from both human and rat studies. Our findings indicate that the time to reach the maximum mAb concentration in the plasma, denoted by Tmax, displays a weak positive correlation with mAb half-life and a negligible correlation with bioavailability. In contrast, the half-life of mAbs exhibits a strong positive correlation with bioavailability. Moreover, the rate of mAb transport from lymph to plasma significantly affects the mAb half-life. Increasing the transport rates of mAbs from the injection site to the lymph or from lymph to plasma enhances bioavailability. These insights, combined with our compartmental model, contribute to a deeper understanding of the pharmacokinetics of subcutaneously administered mAbs.

Toward Characterizing Lymphatic Vasculature in the Mammary Gland During Normal Development and Tumor-Associated Remodeling

Lymphatic vasculature has been shown to promote metastatic spread of breast cancer. Lymphatic vasculature, which is made up of larger collecting vessels and smaller capillaries, has specialized cell junctions that facilitate cell intravasation. Normally, these junctions are designed to collect immune cells and other cellular components for immune surveillance by lymph nodes, but they are also utilized by cancer cells to facilitate metastasis. Although lymphatic development overall in the body has been well-characterized, there has been little focus on how the lymphatic network changes in the mammary gland during stages of remodeling such as pregnancy, lactation, and postpartum involution. In this review, we aim to define the currently known lymphangiogenic factors and lymphatic remodeling events during mammary gland morphogenesis. Furthermore, we juxtapose mammary gland pubertal development and postpartum involution to show similarities of pro-lymphangiogenic signaling as well as other molecular signals for epithelial cell survival that are critical in these morphogenic stages. The similar mechanisms include involvement of M2-polarized macrophages that contribute to matrix remodeling and vasculogenesis; signal transducer and activator of transcription (STAT) survival and proliferation signaling; and cyclooxygenase 2 (COX2)/Prostaglandin E2 (PGE2) signaling to promote ductal and lymphatic expansion. Investigation and characterization of lymphangiogenesis in the normal mammary gland can provide insight to targetable mechanisms for lymphangiogenesis and lymphatic spread of tumor cells in breast cancer.

A dual-clock-driven model of lymphatic muscle cell pacemaking to emulate knock-out of Ano1 or IP3R

Lymphatic system defects are involved in a wide range of diseases, including obesity, cardiovascular disease, and neurological disorders, such as Alzheimer's disease. Fluid return through the lymphatic vascular system is primarily provided by contractions of muscle cells in the walls of lymphatic vessels, which are in turn driven by electrochemical oscillations that cause rhythmic action potentials and associated surges in intracellular calcium ion concentration. There is an incomplete understanding of the mechanisms involved in these repeated events, restricting the development of pharmacological treatments for dysfunction. Previously, we proposed a model where autonomous oscillations in the membrane potential (M-clock) drove passive oscillations in the calcium concentration (C-clock). In this paper, to model more accurately what is known about the underlying physiology, we extend this model to the case where the M-clock and the C-clock oscillators are both active but coupled together, thus both driving the action potentials. This extension results from modifications to the model's description of the IP3 receptor, a key C-clock mechanism. The synchronised dual-driving clock behaviour enables the model to match IP3 receptor knock-out data, thus resolving an issue with previous models. We also use phase-plane analysis to explain the mechanisms of coupling of the dual clocks. The model has the potential to help determine mechanisms and find targets for pharmacological treatment of some causes of lymphoedema.

Transport Barriers Influence the Activation of Anti-Tumor Immunity: A Systems Biology Analysis

Effective anti-cancer immune responses require activation of one or more naïve T cells. If the correct naïve T cell encounters its cognate antigen presented by an antigen presenting cell, then the T cell can activate and proliferate. Here, mathematical modeling is used to explore the possibility that immune activation in lymph nodes is a rate-limiting step in anti-cancer immunity and can affect response rates to immune checkpoint therapy. The model provides a mechanistic framework for optimizing cancer immunotherapy and developing testable solutions to unleash anti-tumor immune responses for more patients with cancer. The results show that antigen production rate and trafficking of naïve T cells into the lymph nodes are key parameters and that treatments designed to enhance tumor antigen production can improve immune checkpoint therapies. The model underscores the potential of radiation therapy in augmenting tumor immunogenicity and neoantigen production for improved ICB therapy, while emphasizing the need for careful consideration in cases where antigen levels are already sufficient to avoid compromising the immune response.

Dynamic Contrast-enhanced CT Lymphangiography to Quantify Thoracic Duct Lymphatic Flow

Background CT lymphangiography has been used to image the lymphatic anatomy and assess lymphatic abnormalities. There is, however, a need to develop a method for quantification of lymphatic flow rate in the thoracic duct (TD). Purpose To develop and validate a TD lymphatic flow measurement technique using dynamic contrast-enhanced CT lymphangiography. Materials and Methods Lymphatic flow rate was measured with two techniques: a first-pass analysis technique based on a single compartment model and a thresholding technique distinguishing between opacified and nonopacified voxels within the TD. The measurements were validated in a swine animal model between November 2021 and September 2022. CT images were acquired at 100 kV and 200 mA using a fast-pitched helical scan mode covering the entire TD following contrast material injection into the bilateral inguinal lymph nodes. Two helical CT scans, acquired at the base and peak contrast enhancement of the TD, were used to measure lymphatic flow rate. A US flow probe surgically placed around the TD provided the reference standard measurement. CT lymphatic flow measurements were compared with the reference US flow probe measurements using regression and Bland-Altman analysis. Repeatability was determined using repeated flow measurements within approximately 10 minutes of each other. Results Eleven swine (10 male; mean weight, 43.6 kg ± 2.6 [SD]) were evaluated with 71 dynamic CT acquisitions. The lymphatic flow rates measured using the first-pass analysis and thresholding techniques were highly correlated with the reference US flow probe measurements (r = 0.99 and 0.91, respectively) and showed good agreement with the reference standard, with Bland-Altman analysis showing small mean differences of 0.04 and 0.05 mL/min, respectively. The first-pass analysis and thresholding techniques also showed good agreement for repeated flow measurements (r = 0.94 and 0.90, respectively), with small mean differences of 0.09 and 0.03 mL/min, respectively. Conclusion The first-pass analysis and thresholding techniques could be used to accurately and noninvasively quantify TD lymphatic flow using dynamic contrast-enhanced CT lymphangiography. © RSNA, 2023 See also the editorial by Choyke in this issue.

Geometry-induced rectification of looped oscillatory flows

In this study, we leverage geometry-induced asymmetries to rectify oscillatory flows and induce net directional transport of fluid in a looped network. We demonstrate this valveless rectification phenomenon in an experimental apparatus that consists of an acrylic flow chamber with a deformable wall connected to a syringe pump via a T-junction. Here, oscillatory flows were forced by the syringe pump. We found that the asymmetries that existed in the geometric configuration of the looped channel could be exploited to generate net directional flow and that this geometric configuration is key in determining the directionality. By varying the pumping parameters in the system, we determined a relationship between the frequency and stroke length of the forcing syringe pump and the resulting directional flow in the loop. Using an analytical model and flow computations, we posit how asymmetric flow separation occurring at the T-junction could explain the observed flows.

Image analysis techniques for in vivo quantification of cerebrospinal fluid flow

Over the past decade, there has been a tremendously increased interest in understanding the neurophysiology of cerebrospinal fluid (CSF) flow, which plays a crucial role in clearing metabolic waste from the brain. This growing interest was largely initiated by two significant discoveries: the glymphatic system (a pathway for solute exchange between interstitial fluid deep within the brain and the CSF surrounding the brain) and meningeal lymphatic vessels (lymphatic vessels in the layer of tissue surrounding the brain that drains CSF). These two CSF systems work in unison, and their disruption has been implicated in several neurological disorders including Alzheimer's disease, stroke, and traumatic brain injury. Here, we present experimental techniques for in vivo quantification of CSF flow via direct imaging of fluorescent microspheres injected into the CSF. We discuss detailed image processing methods, including registration and masking of stagnant particles, to improve the quality of measurements. We provide guidance for quantifying CSF flow through particle tracking and offer tips for optimizing the process. Additionally, we describe techniques for measuring changes in arterial diameter, which is an hypothesized CSF pumping mechanism. Finally, we outline how these same techniques can be applied to cervical lymphatic vessels, which collect fluid downstream from meningeal lymphatic vessels. We anticipate that these fluid mechanical techniques will prove valuable for future quantitative studies aimed at understanding mechanisms of CSF transport and disruption, as well as for other complex biophysical systems.