Lymphatic Contractile Function: A Comprehensive Review of Drug Effects and Potential Clinical Application

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.

Sodium, Interstitium, Lymphatics and Hypertension-A Tale of Hydraulics

Blood pressure is regulated by vascular resistance and intravascular volume. However, exchanges of electrolytes and water between intra and extracellular spaces and filtration of fluid and solutes in the capillary beds blur the separation between intravascular, interstitial and intracellular compartments. Contemporary paradigms of microvascular exchange posit filtration of fluids and solutes along the whole capillary bed and a prominent role of lymphatic vessels, rather than its venous end, for their reabsorption. In the last decade, these concepts have stimulated greater interest in and better understanding of the lymphatic system as one of the master regulators of interstitial volume homeostasis. Here, we describe the anatomy and function of the lymphatic system and focus on its plasticity in relation to the accumulation of interstitial sodium in hypertension. The pathophysiological relevance of the lymphatic system is exemplified in the kidneys, which are crucially involved in the control of blood pressure, but also hypertension-mediated cardiac damage. Preclinical modulation of the lymphatic reserve for tissue drainage has demonstrated promise, but has also generated conflicting results. A better understanding of the hydraulic element of hypertension and the role of lymphatics in maintaining fluid balance can open new approaches to prevent and treat hypertension and its consequences, such as heart failure.

IP3R1 underlies diastolic ANO1 activation and pressure-dependent chronotropy in lymphatic collecting vessels

Pressure-dependent chronotropy of murine lymphatic collecting vessels relies on the activation of the Ca2+-activated chloride channel encoded by Anoctamin 1 (Ano1) in lymphatic muscle cells. Genetic ablation or pharmacological inhibition of ANO1 results in a significant reduction in basal contraction frequency and essentially complete loss of pressure-dependent frequency modulation by decreasing the rate of the diastolic depolarization phase of the ionic pacemaker in lymphatic muscle cells (LMCs). Oscillating Ca2+ release from sarcoendoplasmic reticulum Ca2+ channels has been hypothesized to drive ANO1 activity during diastole, but the source of Ca2+ for ANO1 activation in smooth muscle remains unclear. Here, we investigated the role of the inositol triphosphate receptor 1 (Itpr1; Ip3r1) in this process using pressure myography, Ca2+ imaging, and membrane potential recordings in LMCs of ex vivo pressurized inguinal-axillary lymphatic vessels from control or Myh11CreERT2;Ip3r1fl/fl (Ip3r1ismKO) mice. Ip3r1ismKO vessels had significant reductions in contraction frequency and tone but an increased contraction amplitude. Membrane potential recordings from LMCs of Ip3r1ismKO vessels revealed a depressed diastolic depolarization rate and an elongation of the plateau phase of the action potential (AP). Ca2+ imaging of LMCs using the genetically encoded Ca2+ sensor GCaMP6f demonstrated an elongation of the Ca2+ flash associated with an AP-driven contraction. Critically, diastolic subcellular Ca2+ transients were absent in LMCs of Ip3r1ismKO mice, demonstrating the necessity of IP3R1 activity in controlling ANO1-mediated diastolic depolarization. These findings indicate a critical role for IP3R1 in lymphatic vessel pressure-dependent chronotropy and contractile regulation.

Advances in photoacoustic imaging aided by nano contrast agents: special focus on role of lymphatic system imaging for cancer theranostics

Photoacoustic imaging (PAI) is a successful clinical imaging platform for management of cancer and other health conditions that has seen significant progress in the past decade. However, clinical translation of PAI based methods are still under scrutiny as the imaging quality and clinical information derived from PA images are not on par with other imaging methods. Hence, to improve PAI, exogenous contrast agents, in the form of nanomaterials, are being used to achieve better image with less side effects, lower accumulation, and improved target specificity. Nanomedicine has become inevitable in cancer management, as it contributes at every stage from diagnosis to therapy, surgery, and even in the postoperative care and surveillance for recurrence. Nanocontrast agents for PAI have been developed and are being explored for early and improved cancer diagnosis. The systemic stability and target specificity of the nanomaterials to render its theranostic property depends on various influencing factors such as the administration route and physico-chemical responsiveness. The recent focus in PAI is on targeting the lymphatic system and nodes for cancer diagnosis, as they play a vital role in cancer progression and metastasis. This review aims to discuss the clinical advancements of PAI using nanoparticles as exogenous contrast agents for cancer theranostics with emphasis on PAI of lymphatic system for diagnosis, cancer progression, metastasis, PAI guided tumor resection, and finally PAI guided drug delivery.

Lymphatic muscle cells are unique cells that undergo aging induced changes

Lymphatic muscle cells (LMCs) within the wall of collecting lymphatic vessels exhibit tonic and autonomous phasic contractions, which drive active lymph transport to maintain tissue-fluid homeostasis and support immune surveillance. Damage to LMCs disrupts lymphatic function and is related to various diseases. Despite their importance, knowledge of the transcriptional signatures in LMCs and how they relate to lymphatic function in normal and disease contexts is largely missing. We have generated a comprehensive transcriptional single-cell atlas-including LMCs-of collecting lymphatic vessels in mouse dermis at various ages. We identified genes that distinguish LMCs from other types of muscle cells, characterized the phenotypical and transcriptomic changes in LMCs in aged vessels, and uncovered a pro-inflammatory microenvironment that suppresses the contractile apparatus in advanced-aged LMCs. Our findings provide a valuable resource to accelerate future research for the identification of potential drug targets on LMCs to preserve lymphatic vessel function as well as supporting studies to identify genetic causes of primary lymphedema currently with unknown molecular explanation.

Lymphatic vessels and the renin-angiotensin-system

The lymphatic system is an integral part of the circulatory system and plays an important role in the fluid homeostasis of the human body. Accumulating evidence has recently suggested the involvement of lymphatic dysfunction in the pathogenesis of cardio-reno-vascular (CRV) disease. However, how the sophisticated contractile machinery of lymphatic vessels is modulated and, possibly impaired in CRV disease, remains largely unknown. In particular, little attention has been paid to the effect of the renin-angiotensin-system (RAS) on lymphatics, despite the high concentration of RAS mediators that these tissue-draining vessels are exposed to and the established role of the RAS in the development of classic microvascular dysfunction and overt CRV disease. We herein review recent studies linking RAS to lymphatic function and/or plasticity and further highlight RAS-specific signaling pathways, previously shown to drive adverse arterial remodeling and CRV organ damage that have potential for direct modulation of the lymphatic system.

Fluid Osmolarity Modulates the Rate of Spontaneous Contraction of Lymphatic Vessels and Lymph Flow by Means of a Cooperation between TRPV and VRAC Channels

Lymphatic vessels are capable of sustaining lymph formation and propulsion via an intrinsic mechanism based on the spontaneous contraction of the lymphatic muscle in the wall of lymphatic collectors. Exposure to a hyper- or hypo-osmolar environment can deeply affect the intrinsic contraction rate and therefore alter lymph flow. In this work, we aimed at defining the putative receptors underlying such a response. Functional experiments were conducted in ex vivo rat diaphragmatic specimens containing spontaneously contracting lymphatic vessels that were exposed to either hyper- or hypo-osmolar solutions. Lymphatics were challenged with blockers to TRPV4, TRPV1, and VRAC channels, known to respond to changes in osmolarity and/or cell swelling and expressed by lymphatic vessels. Results show that the normal response to a hyperosmolar environment is a steady decrease in the contraction rate and lymph flow and can be prevented by blocking TRPV1 channels with capsazepine. The response to a hyposmolar environment consists of an early phase of an increase in the contraction rate, followed by a decrease. The early phase is abolished by blocking VRACs with DCPIB, while blocking TRPV4 mainly resulted in a delay of the early response. Overall, our data suggest that the cooperation of the three channels can shape the response of lymphatic vessels in terms of contraction frequency and lymph flow, with a prominent role of TRPV1 and VRACs.

Microcirculatory dysfunction in cardiogenic shock

Cardiogenic shock is usually defined as primary cardiac dysfunction with low cardiac output leading to critical organ hypoperfusion, and tissue hypoxia, resulting in high mortality rate between 40% and 50% despite recent advances. Many studies have now evidenced that cardiogenic shock not only involves systemic macrocirculation, such as blood pressure, left ventricular ejection fraction, or cardiac output, but also involves significant systemic microcirculatory abnormalities which seem strongly associated with the outcome. Although microcirculation has been widely studied in the context of septic shock showing heterogeneous alterations with clear evidence of macro and microcirculation uncoupling, there is now a growing body of literature focusing on cardiogenic shock states. Even if there is currently no consensus regarding the treatment of microcirculatory disturbances in cardiogenic shock, some treatments seem to show a benefit. Furthermore, a better understanding of the underlying pathophysiology may provide hypotheses for future studies aiming to improve cardiogenic shock prognosis.

Intestinal Lymphatic Dysfunction in Kidney Disease

Kidney disease is associated with adverse consequences in many organs beyond the kidney, including the heart, lungs, brain, and intestines. The kidney-intestinal cross talk involves intestinal epithelial damage, dysbiosis, and generation of uremic toxins. Recent studies reveal that kidney injury expands the intestinal lymphatics, increases lymphatic flow, and alters the composition of mesenteric lymph. The intestinal lymphatics, like blood vessels, are a route for transporting potentially harmful substances generated by the intestines. The lymphatic architecture and actions are uniquely suited to take up and transport large macromolecules, functions that differentiate them from blood vessels, allowing them to play a distinct role in a variety of physiological and pathological processes. Here, we focus on the mechanisms by which kidney diseases result in deleterious changes in intestinal lymphatics and consider a novel paradigm of a vicious cycle of detrimental organ cross talk. This concept involves kidney injury-induced modulation of intestinal lymphatics that promotes production and distribution of harmful factors, which in turn contributes to disease progression in distant organ systems.

Chyloperitoneum in Peritoneal Dialysis Secondary to Calcium Channel Blocker Use: Case Series and Literature Review

Chyloperitoneum (chylous ascites) is a rare complication of peritoneal dialysis (PD). Its causes may be traumatic and nontraumatic, associated with neoplastic disease, autoimmune disease, retroperitoneal fibrosis, or rarely calcium antagonist use. We describe six cases of chyloperitoneum occurring in patients on PD as a sequel to calcium channel blocker use. The dialysis modality was automated PD (two patients) and continuous ambulatory PD (the rest of the patients). The duration of PD ranged from a few days to 8 years. All patients had a cloudy peritoneal dialysate, characterized by a negative leukocyte count and sterile culture tests for common germs and fungi. Except for in one case, the cloudy peritoneal dialysate appeared shortly after the initiation of calcium channel blockers (manidipine, n = 2; lercanidipine, n = 4), and cleared up within 24-72 h after withdrawal of the drug. In one case in which treatment with manidipine was resumed, peritoneal dialysate clouding reappeared. Though turbidity of PD effluent is due in most cases to infectious peritonitis, there are other differential causes including chyloperitoneum. Although uncommon, chyloperitoneum in these patients may be secondary to the use of calcium channel blockers. Being aware of this association can lead to prompt resolution by suspension of the potentially offending drug, avoiding stressful situations for the patient such as hospitalization and invasive diagnostic procedures.

Lymphatic Collecting Vessel: New Perspectives on Mechanisms of Contractile Regulation and Potential Lymphatic Contractile Pathways to Target in Obesity and Metabolic Diseases

Obesity and metabolic syndrome pose a significant risk for developing cardiovascular disease and remain a critical healthcare challenge. Given the lymphatic system's role as a nexus for lipid absorption, immune cell trafficking, interstitial fluid and macromolecule homeostasis maintenance, the impact of obesity and metabolic disease on lymphatic function is a burgeoning field in lymphatic research. Work over the past decade has progressed from the association of an obese phenotype with Prox1 haploinsufficiency and the identification of obesity as a risk factor for lymphedema to consistent findings of lymphatic collecting vessel dysfunction across multiple metabolic disease models and organisms and characterization of obesity-induced lymphedema in the morbidly obese. Critically, recent findings have suggested that restoration of lymphatic function can also ameliorate obesity and insulin resistance, positing lymphatic targeted therapies as relevant pharmacological interventions. There remain, however, significant gaps in our understanding of lymphatic collecting vessel function, particularly the mechanisms that regulate the spontaneous contractile activity required for active lymph propulsion and lymph return in humans. In this article, we will review the current findings on lymphatic architecture and collecting vessel function, including recent advances in the ionic basis of lymphatic muscle contractile activity. We will then discuss lymphatic dysfunction observed with metabolic disruption and potential pathways to target with pharmacological approaches to improve lymphatic collecting vessel function.