Matthew D. Nitti

Th2 Cytokines Inhibit Lymphangiogenesis

Lymphangiogenesis is the process by which new lymphatic vessels grow in response to pathologic stimuli such as wound healing, inflammation, and tumor metastasis. It is well-recognized that growth factors and cytokines regulate lymphangiogenesis by promoting or inhibiting lymphatic endothelial cell (LEC) proliferation, migration and differentiation. Our group has shown that the expression of T-helper 2 (Th2) cytokines is markedly increased in lymphedema, and that these cytokines inhibit lymphatic function by increasing fibrosis and promoting changes in the extracellular matrix. However, while the evidence supporting a role for T cells and Th2 cytokines as negative regulators of lymphatic function is clear, the direct effects of Th2 cytokines on isolated LECs remains poorly understood. Using in vitro and in vivo studies, we show that physiologic doses of interleukin-4 (IL-4) and interleukin-13 (IL-13) have profound anti-lymphangiogenic effects and potently impair LEC survival, proliferation, migration, and tubule formation. Inhibition of these cytokines with targeted monoclonal antibodies in the cornea suture model specifically increases inflammatory lymphangiogenesis without concomitant changes in angiogenesis. These findings suggest that manipulation of anti-lymphangiogenic pathways may represent a novel and potent means of improving lymphangiogenesis.

Obesity but not high-fat diet impairs lymphatic function

Background/Objectives:High-fat diet (HFD)-induced obesity has significant negative effects on lymphatic function, but it remains unclear whether this is a direct effect of HFD or secondary to adipose tissue deposition.Methods:We compared the effects of HFD on obesity-prone and obesity-resistant mice and analyzed lymphatic function in vivo and in vitro.Results:Only obesity-prone mice had impaired lymphatic function, increased perilymphatic inflammation and accumulation of lipid droplets surrounding their lymphatic endothelial cells (LECs). LECs isolated from obesity-prone mice, in contrast to obesity-resistant animals, had decreased expression of VEGFR-3 and Prox1. Exposure of LECs to a long-chain free fatty acid increased cellular apoptosis and decreased VEGFR-3 expression, while inhibition of intracellular inhibitors of VEGFR-3 signaling pathways increased cellular viability.Conclusions:Collectively, our studies suggest that HFD-induced obesity decreases lymphatic function by increasing perilymphatic inflammation and altering LEC gene expression. Reversal of diminished VEGFR-3 signaling may rescue this phenotype and improve lymphatic function.

Lymphatic Function Regulates Contact Hypersensitivity Dermatitis in Obesity

Obesity is a major risk factor for inflammatory dermatologic diseases, including atopic dermatitis and psoriasis. In addition, recent studies have shown that obesity impairs lymphatic function. As the lymphatic system is a critical regulator of inflammatory reactions, we tested the hypothesis that obesity-induced lymphatic dysfunction is a key regulator of cutaneous hypersensitivity reactions in obese mice. We found that obese mice have impaired lymphatic function, characterized by leaky capillary lymphatics and decreased collecting vessel pumping capacity. In addition, obese mice displayed heightened dermatitis responses to inflammatory skin stimuli, resulting in both higher peak inflammation and a delayed clearance of inflammatory responses. Injection of recombinant vascular endothelial growth factor-C remarkably increased lymphangiogenesis, lymphatic function, and lymphatic endothelial cell expression of chemokine (C-C motif) ligand 21, while decreasing inflammation and expression of inducible nitrous oxide synthase. These changes resulted in considerably decreased dermatitis responses in both lean and obese mice. Taken together, our findings suggest that obesity-induced changes in the lymphatic system result in an amplified and a prolonged inflammatory response.

Exercise training improves obesity‐related lymphatic dysfunction

Obesity results in perilymphatic inflammation and lymphatic dysfunction. Lymphatic dysfunction in obesity is characterized by decreased lymphatic vessel density, decreased collecting lymphatic vessel pumping frequency, decreased lymphatic trafficking of immune cells, increased lymphatic vessel leakiness and changes in the gene expression patterns of lymphatic endothelial cells. Aerobic exercise, independent of weight loss, decreases perilymphatic inflammatory cell accumulation, improves lymphatic function and reverses pathological changes in gene expression in lymphatic endothelial cells.

Obesity-induced lymphatic dysfunction is reversible with weight loss

Obesity induces lymphatic leakiness, decreases initial lymphatic vessel density, impairs collecting vessel pumping and decreases transport of macromolecules. Obesity results in perilymphatic inducible nitric oxide synthase (iNOS) expression and accumulation of T cells and macrophages. Deleterious effects of obesity on the lymphatic system correlate with weight gain. Weight loss restores lymphatic function in obese animals and decreases perilymphatic iNOS and inflammatory cell accumulation.

Inhibition of Inflammation and iNOS Improves Lymphatic Function in Obesity

Although recent studies have shown that obesity decreases lymphatic function, the cellular mechanisms regulating this response remain unknown. In the current study, we show that obesity results in perilymphatic accumulation of inflammatory cells and that local inhibition of this response with topical tacrolimus, an inhibitor of T cell differentiation, increases lymphatic vessel density, decreases perilymphatic iNOS expression, increases lymphatic vessel pumping frequency, and restores lymphatic clearance of interstitial fluid to normal levels. Although treatment of obese mice with 1400W, a selective inhibitor of iNOS, also improved lymphatic collecting vessel contractile function, it did not completely reverse lymphatic defects. Mice deficient in CD4+ cells fed a high fat diet also gained weight relative to controls but were protected from lymphatic dysfunction. Taken together, our findings suggest that obesity-mediated lymphatic dysfunction is regulated by perilymphatic accumulation of inflammatory cells and that T cell inflammatory responses are necessary to initiate this effect.

Topical tacrolimus for the treatment of secondary lymphedema

Secondary lymphedema, a life-long complication of cancer treatment, currently has no cure. Lymphedema patients have decreased quality of life and recurrent infections with treatments limited to palliative measures. Accumulating evidence indicates that T cells play a key role in the pathology of lymphedema by promoting tissue fibrosis and inhibiting lymphangiogenesis. Here using mouse models, we show that topical therapy with tacrolimus, an anti-T-cell immunosuppressive drug, is highly effective in preventing lymphedema development and treating established lymphedema. This intervention markedly decreases swelling, T-cell infiltration and tissue fibrosis while significantly increasing formation of lymphatic collaterals with minimal systemic absorption. Animals treated with tacrolimus have markedly improved lymphatic function with increased collecting vessel contraction frequency and decreased dermal backflow. These results have profound implications for lymphedema treatment as topical tacrolimus is FDA-approved for other chronic skin conditions and has an established record of safety and tolerability.

Pathophysiology of Lymphedema

Although lymphedema is a common disease, the pathophysiology and underlying cellular changes that regulate lymphatic dysfunction after injury remain poorly understood. This lack of understanding is a major obstacle to development of targeted treatment options. As a result, the mainstay treatment of lymphedema currently is palliative options such as compression and physical therapy. Recent studies have aimed to address this gap in our knowledge and have increased our ability to identify patients who are at risk for developing lymphedema and, more importantly, to develop novel methods to treat this disease. These studies have shown that obesity, radiation, infections, and genetic changes significantly increase the risk of developing secondary or iatrogenic lymphedema. In addition, advances in animal studies have shown that fibrosis and the cellular mechanisms that regulate this process play a key role in the pathogenesis of lymphedema. The purpose of this review is to highlight these advances and identify potential areas for future research.

Abstract 96: Lymphatic Dysfunction Amplifies the Pathological Effects of Obesity in Skin Inflammation

RESULTS: Bony Union: While 100% of the DO group demonstrated bony unions, only 11% of the XDO mandibles were unions. The union rates improved to 64%, 86%, and 93% in the AMF, DFO, and Combined groups, respectively. Biomechanical Testing: Compared to the DO group, the XDO mandibles showed decreased values for YL (25N vs. 48N), FL (22N vs. 62N), and S (240N/mm vs. 795N/mm). With AMF, the values were all increased closer to DO levels (42N, 53N, 301N/ mm, respectively). The DFO group was significantly higher than the XDO group in YL (76N,p=.001), FL (92N,p=.000), and S (885N/mm,p=.020). The Combined group also was significantly higher than XDO for YL (62N,p=.026) and FL (87N,p=.001), but was not statistically significant for S (699N/mm,p=.173). The DFO group demonstrated marginally higher values in all three metrics than the combined group. Additionally, none of the treatment groups were statistically different from the DO group for YL, FL, or S.