Fibrosis worsens chronic lymphedema in rodent tissues

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.

The effect of complex decongestive physiotherapy applied with different compression pressures on skin and subcutaneous tissue thickness in individuals with breast cancer-related lymphedema: a double-blinded randomized comparison trial

PURPOSE

The aim of this study was to evaluate the effect of compression bandage applied with different pressures on the skin and subcutaneous thickness in individuals with breast cancer-related lymphedema (BCRL).

METHODS

21 individuals with stage 2 unilateral BCRL participated in the study. Individuals were randomly allocated into two groups as low-pressure bandage (20-30 mmHg) (n: 11) and high-pressure bandage (45-55 mmHg) (n: 10). Skin and subcutaneous tissue thickness, extremity volume, sleep quality, treatment benefit, and comfort were evaluated by ultrasound from 6 reference points (as hand dorsum, wrist volar, forearm volar, arm volar, forearm dorsum, and arm dorsum), volumetric measurement, Pittsburgh Sleep Quality Index, Patient Benefit Index-Lymphedema, and visual analog scale, respectively. Complex decongestive physiotherapy was applied to both groups. Compression bandage was applied according to their group. Individuals were evaluated at the baseline, 1st session, 10th session, 20th session, and at 3-month follow-up.

RESULTS

Skin thickness decreased significantly in the volar reference points of the extremity in the high-pressure bandage group (p = 0.004, p = 0.031, and p = 0.003). Subcutaneous tissue thickness significantly decreased at all reference points in the high-pressure bandage group (p < 0.05). In the low-pressure bandage group, skin thickness only decreased in the forearm dorsum and the arm dorsum (p = 0.002, p = 0.035) and subcutaneous tissue thickness changed for all points (p < 0.05) except for hand and arm dorsum (p = 0.064, p = 0.236). Edema decreased in a shorter time in the high-pressure bandage group (p < 0.001). No significant differences were found in sleep quality, treatment benefit, and comfort for both groups (p = 0.316, p = 0.300, and p = 0.557, respectively).

CONCLUSION

High pressure was more effective in reducing subcutaneous tissue thickness in the dorsum of hand and arm. The usage of high-pressure can be recommended especially in cases which have edema in the dorsum of hand and arm which is difficult to resolve. Also, high-pressure bandage can provide faster edema resolution and can be used in rapid volume reduction as desired. Treatment outcomes may improve with high-pressure bandage without any impairment in comfort, sleep quality, and treatment benefit.

TRIAL REGISTRATION NUMBER AND DATE

NCT05660590, 12/26/2022 retrospectively registered.

Chronic Progressive Lymphedema in Belgian Draft Horses: Understanding and Managing a Challenging Disease

Chronic progressive lymphedema (CPL) in draft horses is characterized by increased dermal thickness and fibrosis, with the development of skinfolds and nodules, hyperkeratosis, and ulcerations on the distal limbs of affected horses. Secondary bacterial, fungal, or parasitic infections frequently complicate and aggravate the lesions, as well as the progression of this disease. CPL has a particularly high prevalence of up to 85.86% in the Belgian draft horse breed. Due to the disease's progressive and incurable nature, affected horses are often euthanized prematurely. The treatment options are solely symptomatic, aimed at improving the horse's quality of life. Despite the severity of this condition, many uncertainties about its etiology and pathogenesis still remain to date. The established scientific research on CPL is rather limited, although there is an urgent need for strategies to tackle this disease. This review summarizes the available knowledge, serving as a guideline for practitioners, and provides perspectives for future research programs.

Therapeutic Lymphangiogenesis Is a Promising Strategy for Secondary Lymphedema

Secondary lymphedema is caused by lymphatic insufficiency (lymphatic drainage failure) following lymph node dissection during the surgical treatment or radiation therapy of breast or pelvic cancer. The clinical problems associated with lymphedema are reduced quality of life in terms of appearance and function, as well as the development of skin ulcers, recurrent pain, and infection. Currently, countermeasures against lymphedema are mainly physical therapy such as lymphatic massage, elastic stockings, and skin care, and there is no effective and fundamental treatment with a highly recommended grade. Therefore, there is a need for the development of a fundamental novel treatment for intractable lymphedema. Therapeutic lymphangiogenesis, which has been attracting attention in recent years, is a treatment concept that reconstructs the fragmented lymphatic network to recover lymphatic vessel function and is revolutionary to be a fundamental cure. This review focuses on the translational research of therapeutic lymphangiogenesis for lymphedema and outlines the current status and prospects in the development of therapeutic applications.

Can Tissue Stiffness Measured Using Shear-Wave Elastography Represent Lymphedema in Breast Cancer?

Background: Lymphedema causes skin and subcutaneous fibrosis. However, quantitative methods for estimating the severity of fibrosis due to lymphedema have not been established. We evaluated skin stiffness using shear-wave elastography (SWE) and aimed to identify stiffness-associated factors in patients with breast cancer-related lymphedema (BCRL). Methods and Results: Thirty-six women (mean age, 57.5 ± 1.78 years; range, 39-77 years) were retrospectively recruited for this study. The mid-arm and mid-forearm circumferences were measured. The percentage differences in arm and forearm circumferences were used as an indicator of the severity of lymphedema at the time of SWE measurement and the measurement taken when the symptoms were most severe. Not subcutaneous tissues but cutaneous tissues of the affected arm and forearm showed a significant increase in shear-wave velocity (SWV) compared with those of the unaffected side. However, SWV was not correlated with the severity of lymphedema as a percentage difference when symptoms were most severe. Body mass index and lymphedema duration showed no significant correlation with the SWV of cutaneous tissues on the affected upper extremities. Conclusions: SWE can adequately estimate cutaneous fibrosis between the affected and unaffected limbs in patients with BCRL. However, evaluation of subcutaneous fibrosis is limited. Therefore, SWE can be an effective tool for evaluating cutaneous fibrosis in patients with BCRL.

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.

Current Advancements in Animal Models of Postsurgical Lymphedema: A Systematic Review

Significance: Secondary lymphedema is a debilitating disease caused by lymphatic dysfunction characterized by chronic swelling, dysregulated inflammation, disfigurement, and compromised wound healing. Since there is no effective cure, animal model systems that support basic science research into the mechanisms of secondary lymphedema are critical to advancing the field. Recent Advances: Over the last decade, lymphatic research has led to the improvement of existing animal lymphedema models and the establishment of new models. Although an ideal model does not exist, it is important to consider the strengths and limitations of currently available options. In a systematic review adhering to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines, we present recent developments in the field of animal lymphedema models and provide a concise comparison of ease, cost, reliability, and clinical translatability. Critical Issues: The incidence of secondary lymphedema is increasing, and there is no gold standard of treatment or cure for secondary lymphedema. Future Directions: As we iterate and create animal models that more closely characterize human lymphedema, we can achieve a deeper understanding of the pathophysiology and potentially develop effective therapeutics for patients.

Hypoxia and Hypoxia-Inducible Factors in Lymphedema

Lymphedema is a chronic inflammatory disorder characterized by edema, fat deposition, and fibrotic tissue remodeling. Despite significant advances in lymphatic biology research, our knowledge of lymphedema pathology is incomplete. Currently, there is no approved pharmacological therapy for this debilitating disease. Hypoxia is a recognized feature of inflammation, obesity, and fibrosis. Understanding hypoxia-regulated pathways in lymphedema may provide new insights into the pathobiology of this chronic disorder and help develop new medicinal treatments.

Experimental Studies of Latissimus Dorsi Detrusor Myoplasty for Bladder Acontractility: A Systematic Review

Current therapies that allow patients with bladder acontractility to void are limited. The standard therapy is clean intermittent catheterization. Latissimus dorsi detrusor myoplasty (LDDM) has been shown to provide functional contraction and allow patients with bladder acontractility to void voluntarily. Our goal was to summarize experimental studies of LDDM. We hypothesized that experimental studies would show that latissimus dorsi muscle (LDM) flaps for detrusor myoplasty have superior outcomes when compared with other types of flaps. On January 17, 2020, we conducted a systematic review of the PubMed/MEDLINE, Cochrane Clinical Answers, Cochrane Central Register of Controlled Trials, and EMBASE databases, without time frame limitations, to identify articles on the use of LDDM. We excluded studies that investigated other treatments. Of 54 articles identified by the search, three fulfilled the eligibility criteria. A total of 24 dogs underwent procedures and were evaluated with a maximum follow-up of 9 months. Three types of procedures were performed: LDM in situ reconfiguration, LDM myoplasty, and augmentation cystoplasty after supratrigonal cystectomy. Electrical stimulation, cystography, urodynamic and hydrodynamic measurements, and microscopic examinations were performed. Innervated LDM flaps transferred to the bladder were able to contract and promote voiding in response to electrical stimulation. Experimental studies have shown the feasibility of LDDM in canine models. Although no comparison groups were included, innervated LDM flap transferred to the bladder showed promising results regarding contraction capable of voiding.

Two methods of extracorporeal shock-wave therapy in a rat model of secondary lymphedema: a pilot study

Objectives

To compare the effectiveness of two methods of extracorporeal shock-wave therapy (ESWT) in a rat model of forelimb lymphedema, induced by axillary lymph node dissection.

Methods

Sprague–Dawley rats were randomly allocated to a group that received 500 ESWT shocks only in the lymphedematous forelimb (Forelimb/ESWT) and a group that received 300 ESWT shocks in the axilla and 200 shocks in the lymphedematous forelimb (Axilla+Forelimb/ESWT). The circumferences of each limb were then measured. Immunohistochemistry for a pan-endothelial marker (cluster of differentiation [CD]31) and lymphatic vessel endothelial hyaluronan receptor-1, and western blot analysis for vascular endothelial growth factor receptor-3 (VEGFR3) and VEGF-C were performed.

Results

The circumferences of the limbs showed significant effects of group and time following surgery. The circumferences at the carpal joint and 2.5 cm above were smallest in the naïve limbs, larger in the Axilla+Forelimb/ESWT group, and the largest in the control group. VEGFR3 tended to be expressed at a higher level in the Axilla+Forelimb/ESWT group (1.96-fold) than in the Forelimb/ESWT group (1.20-fold) versus the opposite non-edematous forelimbs, although this difference was not statistically significant.

Conclusions

These data suggest that ESWT protocols have differential effects on angiogenesis and lymphangiogenesis in lymphedematous limbs.

Evidence of stage progression in a novel, validated fluorescence-navigated and microsurgical-assisted secondary lymphedema rodent model

Secondary lymphedema (SL)is a frequent and devastating complication of modern oncological therapy and filarial infections. A lack of a reliable preclinical model to investigate the underlying mechanism of clinical stage progression has limited the development of new therapeutic strategies. Current first line treatment has shown to be merely symptomatic and relies on lifetime use of compression garments and decongestive physiotherapy. In this study, we present the development of a secondary lymphedema model in 35 rats using pre- and intraoperative fluorescence-guided mapping of the lymphatics and microsurgical induction. In contrast to the few models reported so far, we decided to avoid the use of radiation for lymphedema induction. It turned out, that the model is nearly free of complications and capable of generating a statistically significant limb volume increase by water displacement measurements, sustained for at least 48 days. A translational, accurate lymphatic dysfunction was visualized by a novel VIS-NIR X-ray ICG-Clearance-Capacity imaging technology. For the first-time SL stage progression was validated by characteristic histological alterations, such as subdermal mast cell infiltration, adipose tissue deposition, and fibrosis by increased skin collagen content. Immunofluorescence confocal microscopy analysis suggested that stage progression is related to the presence of a characteristic α SMA+/HSP-47+/vimentin+ fibroblast subpopulation phenotype. These findings demonstrate that the in-vivo model is a reliable and clinically relevant SL model for the development of further secondary lymphedema therapeutic strategies and the analysis of the veiled molecular mechanisms of lymphatic dysfunction.

The Unresolved Pathophysiology of Lymphedema

Lymphedema is the clinical manifestation of impaired lymphatic transport. It remains an under-recognized and under-documented clinical condition that still lacks a cure. Despite the substantial advances in the understanding of lymphatic vessel biology and function in the past two decades, there are still unsolved questions regarding the pathophysiology of lymphedema, especially in humans. As a consequence of impaired lymphatic drainage, proteins and lipids accumulate in the interstitial space, causing the regional tissue to undergo extensive and progressive architectural changes, including adipose tissue deposition and fibrosis. These changes are also associated with inflammation. However, the temporal sequence of these events, the relationship between these events, and their interplay during the progression are not clearly understood. Here, we review our current knowledge on the pathophysiology of lymphedema derived from human and animal studies. We also discuss the possible cellular and molecular mechanisms involved in adipose tissue and collagen accumulation during lymphedema. We suggest that more studies should be dedicated to enhancing our understanding of the human pathophysiology of lymphedema to pave the way for new diagnostic and therapeutic avenues for this condition.

A retrospective analysis of commonly prescribed medications and the risk of developing breast cancer related lymphedema

Objectives:

Breast cancer related lymphedema (BCRL) is a common complication of current breast cancer treatment modalities, significantly lowering quality of life for these patients and often leading to recurrent infections. Here, based on pre-clinical literature, we aim to retrospectively evaluate the risks of prescribed medications on BCRL development.

Methods:

All post-operative breast cancer patients who received radiotherapy from 2005–2013 at Massachusetts General Hospital and developed lymphedema(n=115) were included in the analysis. Comparable patients without lymphedema(n=230) were randomly selected as control. The following classes of medications were analyzed: NSAIDs, corticosteroids, angiotensin system inhibitors, calcium channel blockers and hormonal therapy. Known risk factors for lymphedema development were included as variables, including BMI, age at diagnosis, type of surgery, number of lymph nodes removed and radiation therapy. Outcomes were BCRL development and lymphedema severity.

Results:

Similarly, to previous studies, we found that an increase in BMI increases the risk of BCRL(p=0.006) and axillary lymph node dissection has a higher risk of developing BCRL compared to sentinel lymph node biopsy(p=0.045). None of the drugs studied increased the risk of BCRL development or lymphedema severity. However, lymphedema severity was positively correlated with the number of lymph nodes removed(p=0.034).

Conclusion:

We found that anti-inflammatory drugs, anti-hypertensive drugs and hormonal therapy taken during the year postoperatively do not increase the risk of BCRL development or lymphedema severity in breast cancer patients. While others have demonstrated that the number of lymph nodes removed during surgery increases the risk of BCRL, we found it also correlates to lymphedema severity.

EW-7197, a Transforming Growth Factor-Beta Type I Receptor Kinase Inhibitor, Ameliorates Acquired Lymphedema in a Mouse Tail Model

Background: Acquired lymphedema is a common consequence of cancer surgery. Fibrosis is one of the main causes of chronic lymphedema since it hinders lymphatic regeneration and this causes a significant decrease in lymphatic flow and accumulation of excessive protein-rich fluid. The transforming growth factor-β1 (TGF-β1) signaling pathway is known in a process of wound repair and fibrosis. In our study, the purpose was to evaluate the efficacy of EW-7197, a peroral TGF-β type I receptor kinase inhibitor, in treating acquired lymphedema. Methods and Results: For lymphedema mouse tail model, we used 10- to 12-week-old female C57BL/6 mice. The skin was circumferentially excised, making a circular band followed by cauterization of lymphatic collecting vessels. Two groups were made in this study: control and treatment. The treatment group (n = 12) received a solution consisting of 0.1 mL of artificial gastric juice and 20 mg/kg EW-7197 by gavage once daily. For evaluation, tail diameter measurement, fluorescence lymphography, and immunofluorescence images were used. EW-7197 treatment ameliorates acquired lymphedema in a mouse tail model by increasing lymphangiogenesis and interstitial flow of the lymphatics by inhibition of the fibrosis. The differences in maximal tail thicknesses between the control and treatment groups were statistically significant from 2 to 4 weeks after surgery. The treatment group showed a greater number of lymphatic vessels at the surgery site than the control group. The treatment group also showed more FITC coverage area at the surgery site. Conclusion: EW-7197 treatment ameliorates acquired lymphedema in a mouse tail model by increasing lymphangiogenesis and interstitial flow.

Mouse tail models of secondary lymphedema: fibrosis gradually worsens and is irreversible

Although the mouse tail model of secondary lymphedema has been widely used in research, our knowledge regarding some of the characteristic changes in this model is lacking. Therefore, in the current study, we aimed to identify pathologic changes after surgery. Tail lymphedema was created in C57BL/6J mice by disconnecting both superficial and deep lymphatic vessels. The surgery resulted in chronic edema formation with the proliferation of subcutaneous adipose tissue, deposition of fibrotic tissue, and gradual increase in CD4⁺ T lymphocyte infiltration. Furthermore, dramatic expansion and an increased number of lymphatic vessels were observed postoperatively. Lymphatic reflux was established at least 8 weeks after surgery, as evidenced by staining of the scar from the surgical excision. In addition, tissue fibrosis was irreversible, although CD4⁺ T cell infiltration, tail swelling, and subcutaneous adipose hyperplasia were alleviated over time. We also show that necrosis could be effectively avoided by paying attention to several details in the modeling process. As animal models play a key role in exploring the pathophysiology of disease, our findings provide strong support for the study of lymphedema. The irreversibility of fibrosis suggests the importance of treating lymphedema by preventing fibrosis development.

Cardiac Lymphatic Dysfunction Causes Drug-Eluting Stent–Induced Coronary Hyperconstricting Responses in Pigs In Vivo

Objective—

We have previously demonstrated that coronary adventitial inflammation plays important roles in the pathogenesis of coronary vasomotion abnormalities, including drug-eluting stent (DES)–induced coronary hyperconstricting responses. Importantly, the adventitia also harbors lymphatic vessels, which may prevent inflammation by transporting extravasated fluid and inflammatory cells. We thus aimed to examine the roles of coronary adventitial lymphatic vessels in the pathogenesis of DES-induced coronary hyperconstricting responses in a porcine model in vivo.

Approach and Results—

We performed 2 experimental studies. In protocol 1, 15 pigs were divided into 3 groups with or without DES and with bare metal stent. Nonstented sites 20 mm apart from stent implantation also were examined. In the protocol 2, 12 pigs were divided into 2 groups with or without lymphatic vessels ligation followed by DES implantation at 2 weeks later (n=6 each). We performed coronary angiography 4 weeks after DES implantation, followed by immunohistological analysis. In protocol 1, the number and the caliber of lymphatic vessels were greater at only the DES edges after 4 more weeks. In protocol 2, coronary hyperconstricting responses were further enhanced in the lymphatic vessels ligation group associated with adventitial inflammation, Rho-kinase activation, and less adventitial lymphatic vessels formation. Importantly, there were significant correlations among these inflammation-related changes and enhanced coronary vasoconstricting responses.

Conclusions—

These results provide evidence that cardiac lymphatic vessel dysfunction plays important roles in the pathogenesis of coronary vasoconstrictive responses in pigs in vivo.

On the complexity of shark bite wounds: From associated bacteria to trauma management and wound repair

The mouth of a shark is a breeding ground for a large variety of bacteria which can easily get transferred onto a human body in the event of a shark bite. Here, we review infections originating from shark oral bacterial flora, which originate from the microbiome of its prey, as well as from the surroundings where an incident takes place. We use the example of an incident which occurred in an aquarium involving a sandtiger shark, Carcharias taurus. In addition to a succinct analysis and interpretation of the wound and recovery process, an overview of currently known bacteria associated with shark bite wounds is given, as well as a summary of the effects of various previously tested antibiotics on bacteria derived from blacktip sharks, Carcharhinus limbatus, bull sharks, C. leucas, and tiger sharks, Galeocerdo cuvier.

LEVEL OF EVIDENCE

Therapeutic study, level V.

Lymphatic Dysfunction, Leukotrienes, and Lymphedema

The lymphatic system is essential for the maintenance of tissue fluid homeostasis, gastrointestinal lipid absorption, and immune trafficking. Whereas lymphatic regeneration occurs physiologically in wound healing and tissue repair, pathological lymphangiogenesis has been implicated in a number of chronic diseases such as lymphedema, atherosclerosis, and cancer. Insight into the regulatory mechanisms of lymphangiogenesis and the manner in which uncontrolled inflammation promotes lymphatic dysfunction is urgently needed to guide the development of novel therapeutics: These would be designed to reverse lymphatic dysfunction, either primary or acquired. Recent investigation has demonstrated the mechanistic role of leukotriene B₄ (LTB₄) in the molecular pathogenesis of lymphedema. LTB₄, a product of the innate immune response, is a constituent of the eicosanoid inflammatory mediator family of molecules that promote both physiological and pathological inflammation. Here we provide an overview of lymphatic development, the pathophysiology of lymphedema, and the role of leukotrienes in lymphedema pathogenesis.

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.

Blood capillary rarefaction and lymphatic capillary neoangiogenesis are key contributors to renal allograft fibrosis in an ACE inhibition rat model

Chronic allograft fibrosis is the major cause of graft loss in kidney transplantation. Progression can only be reduced by inhibition of the renin-angiotensin system (RAS). We tested the hypothesis that the protection provided by angiotensin-converting enzyme (ACE) inhibition also decreases capillary rarefaction, lymphangiogenesis, and podocyte injury in allograft fibrosis. Fisher kidneys were transplanted into bilaterally nephrectomized Lewis rats treated with enalapril (60 mg/kg per day) (ACE inhibitor, ACEi) or vehicle. Proteinuria, blood urea nitrogen, and plasma creatinine were regularly assessed, and grafts were harvested for morphological and immunohistological analysis at various times up to 32 wk. In the vehicle group, many new lymphatic capillaries and severe and diffuse mononuclear infiltration of allografts were observed already 1 wk after transplantation. Lymphangiogenesis increased until week 4, by which time inflammatory infiltration became focal. Lymphatic capillaries were often located at sites of inflammation. Progressive interstitial fibrosis, glomerulosclerosis, capillary rarefaction, and proteinuria appeared later, at weeks 4-12 The number of lymphatic capillary cross sections strongly correlated with the interstitial fibrosis score. Podoplanin immunostaining, a marker of healthy podocytes, disappeared from inflamed or sclerotic glomerular areas. ACEi protected from lymphangiogenesis and associated inflammation, preserved glomerular podoplanin protein expression, and reduced glomerulosclerosis, proteinuria, tubulointerstitial fibrosis, and blood capillary rarefaction at 32 wk. In conclusion, ACEi considerably decreased and/or delayed both glomerulosclerosis and tubulointerstitial injury. Prevention of glomerular podoplanin loss and proteinuria could be attributed to the known intraglomerular pressure-lowering effects of ACEi. Reduction of lymphangiogenesis could contribute to amelioration of tubulointerstitial fibrosis and inflammatory infiltration after ACEi.

The Lymphatic System in Disease Processes and Cancer Progression

Advances in our understanding of the structure and function of the lymphatic system have made it possible to identify its role in a variety of disease processes. Because it is involved not only in fluid homeostasis but also in immune cell trafficking, the lymphatic system can mediate and ultimately alter immune responses. Our rapidly increasing knowledge of the molecular control of the lymphatic system will inevitably lead to new and effective therapies for patients with lymphatic dysfunction. In this review, we discuss the molecular and physiological control of lymphatic vessel function and explore how the lymphatic system contributes to many disease processes, including cancer and lymphedema.

Blunted flow-mediated responses and diminished nitric oxide synthase expression in lymphatic thoracic ducts of a rat model of metabolic syndrome

Shear-dependent inhibition of lymphatic thoracic duct (TD) contractility is principally mediated by nitric oxide (NO). Endothelial dysfunction and poor NO bioavailability are hallmarks of vasculature dysfunction in states of insulin resistance and metabolic syndrome (MetSyn). We tested the hypothesis that flow-dependent regulation of lymphatic contractility is impaired under conditions of MetSyn. We utilized a 7-wk high-fructose-fed male Sprague-Dawley rat model of MetSyn and determined the stretch- and flow-dependent contractile responses in an isobaric ex vivo TD preparation. TD diameters were tracked and contractile parameters were determined in response to different transmural pressures, imposed flow, exogenous NO stimulation by S-nitro-N-acetylpenicillamine (SNAP), and inhibition of NO synthase (NOS) by l-nitro-arginine methyl ester (l-NAME) and the reactive oxygen species (ROS) scavenging molecule 4-hydroxy-tempo (tempol). Expression of endothelial NO synthase (eNOS) in TD was determined using Western blot. Approximately 25% of the normal flow-mediated inhibition of contraction frequency was lost in TDs isolated from MetSyn rats despite a comparable SNAP response. Inhibition of NOS with l-NAME abolished the differences in the shear-dependent contraction frequency regulation between control and MetSyn TDs, whereas tempol did not restore the flow responses in MetSyn TDs. We found a significant reduction in eNOS expression in MetSyn TDs suggesting that diminished NO production is partially responsible for impaired flow response. Thus our data provide the first evidence that MetSyn conditions diminish eNOS expression in TD endothelium, thereby affecting the flow-mediated changes in TD lymphatic function.