A chronic and latent lymphatic insufficiency follows recovery from acute lymphedema in the rat foreleg

Tissue-Engineered Therapeutics for Lymphatic Regeneration: Solutions for Myocardial Infarction and Secondary Lymphedema

The lymphatic system, which regulates inflammation and fluid homeostasis, is damaged in various diseases including myocardial infarction (MI) and breast-cancer-related lymphedema (BCRL). Mounting evidence suggests that restoring tissue fluid drainage and clearing excess immune cells by regenerating damaged lymphatic vessels can aid in cardiac repair and lymphedema amelioration. Current treatments primarily address symptoms rather than underlying causes due to a lack of regenerative therapies, highlighting the importance of the lymphatic system as a promising novel therapeutic target. Here cutting-edge research on engineered lymphatic tissues, growth factor therapies, and cell-based approaches designed to enhance lymphangiogenesis and restore lymphatic function is explored. Special focus is placed on how therapies with potential for immediate lymphatic reconstruction, originally designed for treating BCRL, can be applied to MI to augment cardiac repair and reduce heart failure risk. The integration of these novel treatments can significantly improve patient outcomes by promoting lymphatic repair, preventing pathological remodeling, and offering new avenues for managing lymphatic-associated diseases.

An Evaluation of Lymphedema Using Optical Coherence Tomography: A Rat Limb Model Approach

Lymphedema is a pathology caused by poor lymphatic flow which may lead to complete disability. Currently, precise, non-invasive techniques for quantifying lymphedema are lacking. In this paper, the results of an in vivo assessment of lymphedema via a developed small-animal model using the hindlimbs of rats and an optical coherence tomography (OCT) technique are presented. This model of lymphedema was based on a surgical lymph node resection and subsequent two-step X-ray exposure. The development of lymphedema was verified via the histological examination of tissue biopsies. The properties of the lymphedematous skin were analyzed in vivo and compared with healthy skin via OCT. The main differences observed were (1) a thickening of the stratum corneum layer, (2) a thinning of the viable epidermis layer, and (3) higher signal attenuation in the dermis layer of the lymphedematous skin. Based on the distribution of the OCT signal's intensity in the skin, a machine learning algorithm was developed which allowed for a classification of normal and lymphedematous tissue sites with an accuracy of 90%. The obtained results pave the way for in vivo control over the development of lymphedema.

Development of a rat model of lymphedema and the implantation of a collagen-based medical device for therapeutic intervention

Secondary lymphedema is a common condition among cancer survivors, and treatment strategies to prevent or treat lymphedema are in high demand. The development of novel strategies to diagnose or treat lymphedema would benefit from a robust experimental animal model of secondary lymphedema. The purpose of this methods paper is to describe and summarize our experience in developing and characterizing a rat hindlimb model of lymphedema. Here we describe a protocol to induce secondary lymphedema that takes advantage of micro computed tomography imaging for limb volume measurements and visualization of lymph drainage with near infrared imaging. To demonstrate the utility of this preclinical model for studying the therapeutic benefit of novel devices, we apply this animal model to test the efficacy of a biomaterials-based implantable medical device.

Evaluation of Longitudinal Lymphatic Function Changes upon Injury in the Mouse Tail with Photodynamic Therapy

PURPOSE

The lymphatic system is an essential but often understudied component of the circulatory system in comparison with its cardiovascular counterpart. Such disparity could often be explained by the difficulty in imaging lymphatics and the specialized microsurgical skills that are often required for lymphatic injury models. Recently, it has been shown that verteporfin, a photosensitive drug used for photodynamic therapy (PDT) to ablate the blood vessels, provides a similar effect on lymphatic vessels. Here, we seek to administer verteporfin and perform a modified form of PDT on collecting lymphatics in the mouse tail, a commonly used location for the study of lymphatic disorders, and examine lymphatic remodeling, contractility, and transport in response to the procedure.

METHODS

Mice collecting lymphatics in the tail were injured by PDT through an intradermal injection of verteporfin in the distal tip of the tail followed by light activation on the proximal portion of the tail downstream of the injection site. Lymphatic function was evaluated using a near-infrared (NIR) imaging system weekly for up to 28 days after injury.

RESULTS

PDT resulted in a loss in lymphatic function contractile frequency that persisted for up to 7 days after injury. Packet transport and packet amplitude, measurements reflective of the strength of contraction, were significantly reduced 14 days after injury. The lymphatics showed a delayed increase in lymphatic leakage at 7 days that persisted until the study endpoint on day 28.

CONCLUSION

This technique provides an easy-to-use method for injuring lymphatics to understand their remodeling response to injury by PDT as well as potentially for screening therapeutics that seek to normalize lymphatic permeability or contractile function after injury.

Temporal Changes in Subcutaneous Fibrosis in Patients with Lower Extremity Lymphedema Following Surgery for Gynecologic Cancer: A Computed Tomography-Based Quantitative Analysis

Lymphedema causes inflammation, which provokes fibrosis within the epifascial tissue. Temporal change in fibrosis according to severity of the lymphedema has not been widely investigated. We aimed to study the quantitative changes in epifascial fibrosis during lymphedema treatment using computed tomography (CT). Forty-five patients (mean age: 57.75 ± 11.12 years) who developed lymphedema following gynecologic surgery were included in this retrospective study. Two weeks of complete decongestive therapy and continued self-bandaging or compression garments were prescribed under regular follow-up monitoring. Lower-extremity epifascial fibrosis was quantitatively analyzed on the initial and follow-up CT scans. Circumference, skin fibrosis, subcutaneous tissue, and fibrosis ratio were calculated in the axial scan. Based on the change in lymphedema severity, we divided subjects into ‘improved’ and ‘aggravated’ groups. The affected lower extremities showed higher circumference, more skin fibrosis and subcutaneous tissue, and higher fibrosis ratio than the unaffected sides on initial CT scan. At follow-up, compared to the aggravated group, the improved group showed significant decreases in fibrosis of skin and subcutaneous tissue and fibrosis ratio. Subcutaneous fibrosis was reversible with volume resolution of lymphedema. Therapeutic approaches should be established on the basis of the reversible nature of fibrotic changes in patients with lower extremity lymphedema.

Study of the antioxidant status in patients with secondary lymphedema of the lower extremities under conservative treatment

Aim. To assess the antioxidant status in patients with secondary lymphedema of the lower extremities who undergo different types of conservative treatment. Methods. The study included 90 patients with secondary lymphedema of the lower extremities and 30 healthy volunteers. Group 1 participants (n=30) received compression therapy and Vitamin E at a dose of 400 IU/day, group 2 participants (n=30) compression therapy and a micronized purified flavonoid fraction 1000 mg/day, group 3 (n=30) compression therapy alone. Group 4 (n=30) comprised healthy volunteers. The level of malondialdehyde, the activity of superoxide dismutase, glutathione peroxidase, catalase, and the level of non-protein thiols (SH-groups) were determined at inclusion in the study and then after 1 and 3 months. Results. In patients with secondary lymphedema, the initial level of glutathione peroxidase was higher by 768.22%, catalase by 420.5%, malondialdehyde by 60%, and the level of SH-groups was lower by 65,71% compared with the group of volunteers. In the first group, there was a significant decrease of 36.1% in the level of superoxide dismutase and a significant increase of 89.9% in the level of glutathione peroxidase at the end of therapy when compared with the level after 1 month. In the second group, catalase level significantly increased by 33.3%, superoxide dismutase by 17.6%, and glutathione peroxidase by 61.3% compared to baseline values. The biochemical indicators of the endothelium significantly increased when using a combination of micronized purified flavonoid fraction and elastic compression in comparison with elastic compression alone and a combination with Vitamin E. In the third group, there were no significant differences in the levels of biochemical indicators of endothelial function. Conclusion. Increased formation of lipid peroxidation products along with a decrease in the activity of antioxidant systems was revealed in patients with lower extremity secondary lymphedema compared with healthy volunteers; the most effective therapy aimed at correcting endothelial cell dysfunction is the use of micronized purified flavonoid fraction and elastic compression.

A novel mouse tail lymphedema model for observing lymphatic pump failure during lymphedema development

It has been suggested that many forms of secondary lymphedema in humans are driven by a progressive loss of lymphatic pump function after an initial risk-inducing event. However, the link between pump failure and disease progression has remained elusive due to experimental challenges in the clinical setting and a lack of adequate animal models. Using a novel surgical model of lymphatic injury, we track the adaptation and functional decline of the lymphatic network in response to surgery. This model mimics the histological hallmarks of the typical mouse tail lymphedema model while leaving an intact collecting vessel for analysis of functional changes during disease progression. Lymphatic function in the intact collecting vessel negatively correlated with swelling, while a loss of pumping pressure generation remained even after resolution of swelling. By using this model to study the role of obesity in lymphedema development, we show that obesity exacerbates acquired lymphatic pump failure following lymphatic injury, suggesting one mechanism through which obesity may worsen lymphedema. This lymphatic injury model will allow for future studies investigating the molecular mechanisms leading to lymphedema development.

Lymphatic pumping: mechanics, mechanisms and malfunction

A combination of extrinsic (passive) and intrinsic (active) forces move lymph against a hydrostatic pressure gradient in most regions of the body. The effectiveness of the lymph pump system impacts not only interstitial fluid balance but other aspects of overall homeostasis. This review focuses on the mechanisms that regulate the intrinsic, active contractions of collecting lymphatic vessels in relation to their ability to actively transport lymph. Lymph propulsion requires not only robust contractions of lymphatic muscle cells, but contraction waves that are synchronized over the length of a lymphangion as well as properly functioning intraluminal valves. Normal lymphatic pump function is determined by the intrinsic properties of lymphatic muscle and the regulation of pumping by lymphatic preload, afterload, spontaneous contraction rate, contractility and neural influences. Lymphatic contractile dysfunction, barrier dysfunction and valve defects are common themes among pathologies that directly involve the lymphatic system, such as inherited and acquired forms of lymphoedema, and pathologies that indirectly involve the lymphatic system, such as inflammation, obesity and metabolic syndrome, and inflammatory bowel disease.

High-resolution 3D volumetry versus conventional measuring techniques for the assessment of experimental lymphedema in the mouse hindlimb

Secondary lymphedema is a common complication of cancer treatment characterized by chronic limb swelling with interstitial inflammation. The rodent hindlimb is a widely used model for the evaluation of novel lymphedema treatments. However, the assessment of limb volume in small animals is challenging. Recently, high-resolution three-dimensional (3D) imaging modalities have been introduced for rodent limb volumetry. In the present study we evaluated the validity of microcomputed tomography (μCT), magnetic resonance imaging (MRI) and ultrasound in comparison to conventional measuring techniques. For this purpose, acute lymphedema was induced in the mouse hindlimb by a modified popliteal lymphadenectomy. The 4-week course of this type of lymphedema was first assessed in 6 animals. In additional 12 animals, limb volumes were analyzed by μCT, 9.4 T MRI and 30 MHz ultrasound as well as by planimetry, circumferential length and paw thickness measurements. Interobserver correlation was high for all modalities, in particular for μCT analysis (r = 0.975, p < 0.001). Importantly, caliper-measured paw thickness correlated well with μCT (r = 0.861), MRI (r = 0.821) and ultrasound (r = 0.800). Because the assessment of paw thickness represents a time- and cost-effective approach, it may be ideally suited for the quantification of rodent hindlimb lymphedema.

Anatomical Effects of Axillary Nodes Dissection on Rat Lymphatic System Model: Indocyanine Green Mapping and Dissection

BACKGROUND

Axillary nodes dissection (AND) is an important risk factor for the appearance of breast cancer-related lymphedema (BCRL). The anatomy and pathophysiology leading to the development of BCRL after AND are not completely understood. Despite the existence of lymphedema models after AND, none of them were able to create lymphedemas without additional chemical inflammatory drugs or auxiliary physical techniques (radiotherapy). In this study, we aimed to describe the anatomical changes of AND on a rat's front leg before and after a new surgery technique.

METHODS AND RESULTS

AND was performed on seven Wistar rats with a new, posterior surgical approach. Indocyanine green mapping was done before and after surgery to detect "normal and secondary superficial lymphatic pathways" of the operated rat's front legs. Twelve months after surgery, dissections were performed. Subcutaneous blue dye injection of the hand was used to observe superficial and deep lymphatic pathways. Postsurgery, an acute edema of arm and shoulder appeared and persisted for 14-21 days. However, none of the rats showed a chronic secondary lymphedema. In two cases, seromas also appeared. All rats showed substitution functional lymphatic pathways as perforating lymph vessels around the surgical sites.

CONCLUSION

This is the first description of perforating lymph vessels as lymphatic substitution pathways after AND on rats. These results help to understand why a chronic secondary lymphedema could not be created in rats after AND without additional chemical or physical interventions.

Characterization of internodal collecting lymphatic vessel function after surgical removal of an axillary lymph node in mice

Secondary lymphedema is an acquired lymphatic disorder, which occurs because of damage to the lymphatic system from surgery and/or radiation therapy for cancer treatment. However, it remains unknown how post-nodal collecting lymphatic vessels (CLVs) draining to the surgical wound area change in response to lymphadenectomy. We investigated functional and architectural changes of inguinal-to-axillary internodal CLVs (ICLVs) in mice after a single axillary LN (ALN) dissection using near-infrared fluorescence imaging. Our data showed no lymph flow in the ICLVs draining from the inguinal LN (ILN) at 2 days post-surgery. External compression enabled visualization of a small segment of contractile fluorescent ICLVs, but not all the way to the axillary region. At day 6, abnormal lymphatic drainage patterns, including lateral and retrograde lymph flow via vessels branching off the ICLVs were observed, which started to disappear beginning 9 days after surgery. The administration of vascular endothelial growth factor (VEGF)-C into the wound increased resolution of altered lymphatic drainage. Lymphatic drainage from the base of the tail to the ILN did not significantly change over time. These results demonstrate that lymph flow in the CLVs is dramatically affected by a LN dissection and long-term interruption of lymph flow might cause CLV dysfunction and thus contribute to chronic lymphatic disorders.

Engendering allograft ignorance in a mouse model of allogeneic skin transplantation to the distal hind limb

OBJECTIVE

The aim of this study was to demonstrate lymphatic isolation in a model of hind limb lymph node (LN) excision, consisting of ipsilateral popliteal and inguinal LN excision and to evaluate the immunologic response to allogeneic skin transplanted onto this region of lymphatic isolation.

METHODS

To study lymphatic flow, C57BL/6 mice underwent lymphadenectomy (n = 5), sham lymphadenectomy (n = 5), or no intervention (n = 5), followed by methylene blue injection. Mice were dissected to determine whether methylene blue traveled to the iliac LN. To study host response to skin transplantation, C57BL/6 mice underwent allogeneic skin transplantation with LN excision (n = 6), allogeneic skin transplantation alone (n = 6), or syngeneic skin transplantation (n = 4). Skin grafts were placed distal to the popliteal fossa and mice were euthanized at day 10. Grafts were stained for endothelial cell and proliferation markers (CD31 and Ki67, respectively). Secondary lymphoid tissues (spleen, ipsilateral axillary LN, and contralateral inguinal LN) were removed and rechallenged with BALB/c alloantigen in vitro with subsequent assay of interferon-γ and interleukin 4 cell expression using ELISPOT technique.

RESULTS

Mice that underwent LN excision had no evidence of methylene blue in the iliac nodes; mice without surgical intervention or with sham LN excision consistently had methylene blue visible in the ipsilateral iliac nodes. Mice treated with allogeneic skin transplantation and LN excision had lower expression of interferon-γ and interleukin 4 in the secondary lymphoid tissues.

CONCLUSIONS

Lymph node excision completely interrupts lymphatic flow of the hind limb. This model of lymphatic isolation impairs the ability of the transplant recipient to acutely mount a Th1 or Th2 response to allogeneic skin transplants.

Fibrosis worsens chronic lymphedema in rodent tissues

Secondary lymphedema in humans is a common consequence of lymph node dissection (LND) to treat breast cancer. A peculiar characteristic of the disease is that lifelong swelling often precipitously appears several years after the surgical treatment, often due to an inflammatory stimulus. Although the incidence of secondary lymphedema dramatically increases after radiation therapy, the relationship between fibrotic scarring and the eventual appearance of lymphedema remains unclear. To clarify the role of fibrosis in secondary lymphedema initiation, we chemically increased fibrosis in rodent tissues with bleomycin and assessed the ability of the local lymphatic system to prevent lymphedema, either acutely or in a chronic state induced by inflammation. We found that bleomycin injections exacerbated fibrotic matrix deposition in an acute mouse tail lymphedema model (P < 0.005), reduced wound closure (P < 0.005), and impaired the ability of tail lymphatics to regenerate (P < 0.005) and reduce the swelling (P < 0.05). When fibrosis was worsened with bleomycin after axillary LND in the rat foreleg, the ability of the foreleg lymphatic system to reduce the chronic state swelling induced by stimulated inflammation was severely impaired (P < 0.005). Indocyanine green lymphography in axillary LND-recovered rat forelegs revealed a worsened lymphatic drainage due to inflammation and bleomycin pretreatment. Although inflammation reduced the drainage of dextran fluid tracer from control forelegs (P < 0.05), the reduction in fluid drainage was more severe after axillary LND when fibrosis was first increased (P < 0.005). These findings demonstrate that fibrosis reduces the lymphatic capacity to functionally regenerate and prevent the chronic appearance of lymphedema.

Bridging the divide between pathogenesis and detection in lymphedema

While our understanding of the lymphatic system has improved substantially in the past few decades, the translation of this knowledge into improved healthcare solutions for patients suffering from secondary lymphedema has been severely limited. The challenge facing clinicians is two-fold. First, there is no reliable, affordable, diagnostic capable of detecting the disease before symptoms of the lymphedema develop and the efficacy of treatment options becomes limited. Second, our understanding of the disease pathogenesis, its risk factors, and the underlying physiologic mechanisms is still in its infancy. These two challenges go hand in hand as limited diagnostic options have hindered our ability to understand lymphedema progression, and the lack of known underlying mechanisms involved in the disease prohibits the development of new diagnostic targets. This review serves to discuss the recent developments in clinical and lab research settings of both lymphedema diagnostic technologies and our understanding of the mechanisms driving disease risk and progression. We will show how these two lines of research are synergistically working with the ultimate goal of improving patient outcomes for those suffering from this horrible disease, identifying key areas of further research that are warranted to move the field forward and provide clinical relief for this neglected patient population.

Spatio-temporal changes of lymphatic contractility and drainage patterns following lymphadenectomy in mice

Objective

To investigate the redirection of lymphatic drainage post-lymphadenectomy using non-invasive near-infrared fluorescence (NIRF) imaging, and to subsequently assess impact on metastasis.

Background

Cancer-acquired lymphedema arises from dysfunctional fluid transport after lymphadenectomy performed for staging and to disrupt drainage pathways for regional control of disease. However, little is known about the normal regenerative processes of the lymphatics in response to lymphadenectomy and how these responses can be accelerated, delayed, or can impact metastasis.

Methods

Changes in lymphatic “pumping” function and drainage patterns were non-invasively and longitudinally imaged using NIRF lymphatic imaging after popliteal lymphadenectomy in mice. In a cohort of mice, B16F10 melanoma was inoculated on the dorsal aspect of the paw 27 days after lymphadenectomy to assess how drainage patterns affect metastasis.

Results

NIRF imaging demonstrates that, although lymphatic function and drainage patterns change significantly in early response to popliteal lymph node (PLN) removal in mice, these changes are transient and regress dramatically due to a high regenerative capacity of the lymphatics and co-opting of collateral lymphatic pathways around the site of obstruction. Metastases followed the pattern of collateral pathways and could be detected proximal to the site of lymphadenectomy.

Conclusions

Both lymphatic vessel regeneration and co-opting of contralateral vessels occur following lymphadenectomy, with contractile function restored within 13 days, providing a basis for preclinical and clinical investigations to hasten lymphatic repair and restore contractile lymphatic function after surgery to prevent cancer-acquired lymphedema. Patterns of cancer metastasis after lymphadenectomy were altered, consistent with patterns of re-directed lymphatic drainage.

Developing a Lower Limb Lymphedema Animal Model with Combined Lymphadenectomy and Low-dose Radiation

Background:

This study was aimed to establish a consistent lower limb lymphedema animal model for further investigation of the mechanism and treatment of lymphedema.

Methods:

Lymphedema in the lower extremity was created by removing unilateral inguinal lymph nodes followed by 20, 30, and 40 Gy (groups IA, IB, and IC, respectively) radiation or by removing both inguinal lymph nodes and popliteal lymph nodes followed by 20 Gy (group II) radiation in Sprague-Dawley rats (350–400 g). Tc⁹⁹ lymphoscintigraphy was used to monitor lymphatic flow patterns. Volume differentiation was assessed by microcomputed tomography and defined as the percentage change of the lesioned limb compared to the healthy limb.

Results:

At 4 weeks postoperatively, 0% in group IA (n = 3), 37.5% in group IB (n = 16), and 50% in group IC (n = 26) developed lymphedema in the lower limb with total mortality and morbidity rate of 0%, 56.3%, and 50%, respectively. As a result of the high morbidity and mortality rates, 20 Gy was selected, and the success rate for development of lymphedema in the lower limb in group II was 81.5% (n = 27). The mean volume differentiation of the lymphedematous limb compared to the health limb was 7.76% ± 1.94% in group II, which was statistically significant compared to group I (P < 0.01).

Conclusions:

Removal of both inguinal and popliteal lymph nodes followed by radiation of 20 Gy can successfully develop lymphedema in the lower limb with minimal morbidity in 4 months.

Lymphatic vascular response to acute inflammation

During acute inflammation, functioning lymphatics are believed to reduce edema and to provide a transiting route for immune cells, but the extent at which the dermal lymphatic remodeling impacts lymphatic transport or the factors regulating these changes remains unclear. Herein we quantify the increase in lymphatic endothelial cells (LECs) and examine the expression of pro-angiogenenic and lymphangiogenic factors during acute cutaneous hypersensitivity (CHS). We found that LECs actively proliferate during CHS but that this proliferation does not affect the lymphatic vessel density. Instead, lymphatic remodeling is accompanied by lymphatic vessel leakiness and lower ejection of lymph fluid, which is observed only in the proximal lymphatic vessel draining the inflamed area. LECs and the immune cells release growth factors and cytokines during inflammation, which impact the lymphatic microenvironment and function. We identified that FGF-2, PLGF-2, HGF, EGF, and KC/CXCL17 are differentially expressed within tissues during acute CHS, but both VEGF-C and VEGF-D levels do not significantly change. Our results indicate that VEGF-C and VEGF-D are not the only players and other factors may be responsible for the LECs proliferation and altered lymphatic function in acute CHS.